Richard Mayer | The University of Georgia (original) (raw)
Papers by Richard Mayer
Postharvest Biology and Technology, 1995
Cucumber (Cucumb sufivus cv. Dasher 3) fruit were immersed in water at 25,38, or 42°C for 30 min ... more Cucumber (Cucumb sufivus cv. Dasher 3) fruit were immersed in water at 25,38, or 42°C for 30 min prior to storage at 12 (nonchilling) or 2S"C (chilling) for two weeks to determine the effects of these treatments on chilling-induced changes in electrolyte leakage, and COz, and ethylene evolution. Storage at 2S"C resulted in a significant increase in electrolyte leakage, which decreased significantly as immersion temperature increased. Chilled fruit had higher rates of CO2 production than did nonchilled fruit following transfer to 21"C, but there was no difference due to immersion temperature. Following transfer to 21"C, nonchilled fruit produced no detectable ethylene whereas chilled fruit produced significant amounts of ethylene. The amount of chilling-induced ethylene production decreased with increased temperature of immersion, and this difference persisted for at least 72 h after transfer to 21°C. The amount of l-aminocyclopropane-1-carboxylic acid (ACC) was significantly higher in chilled than in nonchilled fruit although the amount of ACC in chilled fruit decreased significantly as immersion temperature increased. Nonchilled fruit had significantly higher ACC oxidase activity than did chilled fruit at the time of transfer to 21"C, and ACC oxidase activity decreased as immersion temperature increased.
Journal of Medical Entomology, 1984
... Another key step in the digestive process of he-matophagous insects is the lysis of the eryth... more ... Another key step in the digestive process of he-matophagous insects is the lysis of the erythrocytes. ... More recently the mechanism of midgut hemolysis of the stable fly was characterized by Spates et al. (1982). In the present study the hemolysin of the horn fly is investigated. ...
Toxicology, 1984
Diflubenzuron (DFB) significantly inhibited the uptake of uridine, adenosine, and cytidine but no... more Diflubenzuron (DFB) significantly inhibited the uptake of uridine, adenosine, and cytidine but not thymidine, in cultured Harding-Passey melanoma cells. Inhibition of nucleoside uptake was rapid (i.e., <_ 5 min) and could not be reversed by washing. These results suggest that DFB may affect membrane properties and-as shown by in vivo tests-growth of melanoma cells.
Archives of Biochemistry and Biophysics, 1987
Biochemistry, 1972
1-(5-Dimethylaminonaphthalene-1-sulfonamide)-3-N,N-dimethylaminopropane and 1-(5-dimethylarninona... more 1-(5-Dimethylaminonaphthalene-1-sulfonamide)-3-N,N-dimethylaminopropane and 1-(5-dimethylarninonaphthalene-1-sulfonamido)propane-3-trimethylammonium iodide are active-site-directed, equilibrium fluorescent probes. They are competitive inhibitors of horse serum cholinesterase (3.1.1.8). The basic group in each probe molecule binds at the anionic site. Subsequent binding of the fluorescent moiety is directed to an adjacent, hydrophobic site. Equilibrium dynamics of interaction of the probe-enzyme complexes were
Mutation Research Letters, 1985
1. Mutat Res. 1985 Mar;142(3):127-31. Measurement of cytochrome P-450 dependent dealkylation of a... more 1. Mutat Res. 1985 Mar;142(3):127-31. Measurement of cytochrome P-450 dependent dealkylation of alkoxyphenoxazones in hepatic S9s and hepatocyte homogenates: effects of dicumarol. Lubet RA, Nims RW, Mayer RT, Cameron JW, Schechtman LM. ...
Journal of Microscopy, 1974
The construction of a microspectrofluorometer with automatic correction capabilities is given. Th... more The construction of a microspectrofluorometer with automatic correction capabilities is given. The instrument uses a quantum counting system for correction of excitation spectra and an interpolating function generator for correction of emission spectra. An inexpensive analogue computer is an integral part of the electronic portion of the instrument and allows a number of mathematical manipulations to be performed on the sample and reference signals prior to recording or display. Under the conditions stated, the sensitivity of the instrument is in the 10−9 M range for quinine sulphate irradiated at 365 nm. The linear response range for quinine sulphate is 10−3 to 10−9 M. The operational wavelength range of the machine is between 226 and 700 nm.
Environmental Entomology, 2002
The biological effects of a commercially available neem seed extract (Neemix. 4.5, 4.5% azadirach... more The biological effects of a commercially available neem seed extract (Neemix. 4.5, 4.5% azadirachtin, AZ) were assessed on the brown citrus aphid, Toxoptera citricida (Kirklady), a recently introduced insect pest of citrus in the United States and its parasitoid, Lysiphlebus testaceipes. When small citrus seedlings were dipped with the neem extract at 11Ð180 ppm AZ, 0 Ð 8% of nymphs and 0 Ð17.5% of adults survived 7 d after the treatment while 95% of nymphs and 42.5% of adults in the control survived for the same period. The extract drastically reduced longevity of both adults and nymphs, adult fecundity, and molting of nymphs at all tested concentrations. Spraying neem extract (11Ð180 ppm AZ) onto potted citrus plants in the greenhouse also signiÞcantly reduced aphids by 20 Ð100%, while control aphid populations increased by 950% 7 d after treatment. Application of the extract had little impact on the survival of adult parasitoids and developing parasitoids within aphids because parasite emergences were similar between treated and untreated parasitized aphids. These results indicate that neem extract may be compatible with integrated pest management programs in citrus and should be evaluated for Þeld efÞcacy.
British Journal of Clinical Pharmacology, 1992
The O-dealkylation of seven 7-alkoxyquinoline derivatives by human hepatic and placental microsom... more The O-dealkylation of seven 7-alkoxyquinoline derivatives by human hepatic and placental microsomes and the effect of maternal cigarette smoking on placental 7alkoxyquinoline metabolism was studied. 2 None of several monoclonal antibodies to isoenzymes of cytochrome P450 had a clear effect on metabolism of the compounds by liver microsomes. 3 Maternal cigarette smoking induced the O-dealkylation of all of the 7-alkoxyquinoline derivatives, being greatest for 7-butoxyand 7-benzyloxyquinoline. 4 Placental 7-alkoxyquinoline metabolism induced by smoking was partially inhibited by the monoclonal antibody 1-7-1 raised against 3-methylcholanthrene-induced rat liver P450. 5 None of the 7-alkoxyquinoline O-dealkylations could be assigned specifically to any known P450 isoenzyme in human liver or placenta.
Analytical Biochemistry, 1992
A quantitative fluorometric assay for chitosanase activity in bacterial and plant tissues was dev... more A quantitative fluorometric assay for chitosanase activity in bacterial and plant tissues was developed. The assay can be conducted with either finely milled preparations of chitosan in suspension or dissolved chitosan; activity is based on measurements of glucosamine (GlcN) or oligomers of GlcN. GlcN is detected fluorometrically after reaction with fluorescamine with detection in the nanomole range. Fluorescence measurements of chitosanase activity and radioassay of chitinase in commercial preparations of chitinase from Streptomyces griseus revealed that both activities were present. Specific activities for the S. griseus chitosanase using suspended and soluble chitosans were respectively 1.24 and 6.4 mumol GlcN.min-1.mg protein-1. Specific activity of the S. griseus chitinase was 0.98 mumol GlcN.min-1.mg protein-1. Sweet orange callus tissue was tested for chitosanase and chitinase activity. It was necessary to remove small amine-containing molecules from the callus preparations before chitosanase activity could be assayed. The specific activity for chitinase and chitosanase in desalted extracts of nonembryogenic Valencia sweet orange callus tissue was determined to be 18.6 and 89.4 nmol GlcN.min-1.mg protein-1, respectively.
Biochemical Journal, 1986
The properties of five structurally related forms of cytochrome P-450 (PB1a, PB1b, PB2a, PB2b and... more The properties of five structurally related forms of cytochrome P-450 (PB1a, PB1b, PB2a, PB2b and PB2d) isolated from rats treated with phenobarbital have been compared with two forms isolated previously now termed ‘PB1c’ and ‘PB2c’ These enzymes were characterized by their marginal inducibility by phenobarbital and are clearly distinguishable from the major phenobarbital-inducible proteins. PB1a and PB1b differed in Mr (52,700 and 52,900), absorption spectra and papain-proteolysis fragments. However, they had identical N-terminal sequences. PB2a, PB2b and PB2d had apparent Mr values of 52,900, 52,900 and 50,800. PB2a and PB2b had different N-terminal sequences and, after digestion with papain, gave different papain-proteolysis fragments. The N-terminal sequence of PB2b was similar to, but not identical with, that of pregnenolone-16 alpha-carbonitrile-inducible P-450 species, and PB2b was the protein most closely related to PB2c. The extent of immunocross-reactivity among the forms ...
Journal of Polymer Science Part A-1: Polymer Chemistry, 1970
ABSTRACT Fluorescent probes which are active-site-directed, reversible, competitive inhibitors of... more ABSTRACT Fluorescent probes which are active-site-directed, reversible, competitive inhibitors of serum cholinesterase (ChE) enzymes have been designed and synthesized. Reversible inhibitors of enzyme active sites have a unique importance when they act as fluorescent probes, allowing fluorescence spectroscopic detection of conformation changes and activesite dynamics. 5-Dimethylamino-naphthalene-1-sulfonamido-N,N-dimethyl-n-propyl-amine and its aliphatic quaternary derivative are fluorescent probes for serum cholinesterase. The quaternary probe forms complexes with acetylcholinesterase (AChE). The dissociation constants Kd for the two probes with serum ChE are 6.0 × 10−7 and 6.5 × 10−7M. The inhibition constants Ki are 3.1 × 10−6 and 6.3 × 10−6M from the slopes of Lineweaver-Burk plots. The Michelis constant Km for the enzyme was 8.8 × 10−4M.
Methods in Enzymology, 1978
Publisher Summary This chapter focuses on the direct fluorometric methods for measuring mixed-fun... more Publisher Summary This chapter focuses on the direct fluorometric methods for measuring mixed-function oxidase activity. Ullrich and Weber developed a direct fluorometric method to measure the mouse liver microsomal cytochrome-P-450-dependent O-dealkylation of 7-ethoxycoumarin to yield 7-hydroxycoumarin. Recently, Burke and Mayer described a direct fluorometric assay to measure the O-dealkylation of ethoxyresorufin. The broad substrate specificity and ready induction of the monooxygenase has allowed the development of a large number of specific assays for the enzyme system. Many of the methods require solvent extraction of metabolites and subsequent analysis to quantitate the concentration of the metabolite. The number of manipulations required in these assay methods and the problems involved in solvent extraction of compounds of intermediate polarity complicates and extends the time required for analysis of enzyme activity. Several direct spectrophotometric and spectrophotofluorimetric assays are developed to obviate these problems, and two fluorescent assays are encapsulated in this chapter.
Drug metabolism and disposition: the biological fate of chemicals
Page 1. Send reprint requests to: Dr. MD Burke. Biochemistry Department. The University of Texas ... more Page 1. Send reprint requests to: Dr. MD Burke. Biochemistry Department. The University of Texas Health Science Center. 5323 Harry Hines Blvd.. Dallas, Texas 75235 583 DRUG METABOLISM AND DIsPosITIoN Copyright ...
Drug metabolism and disposition: the biological fate of chemicals
Certain characteristics of ethoxyresorufin O-de-ethylation, as catalyzed by microsomes of liver, ... more Certain characteristics of ethoxyresorufin O-de-ethylation, as catalyzed by microsomes of liver, lung, and intestine of control and pretreated rats and hamsters, were studied. The results support previous suggestions that the reaction is catalyzed primarily by a 3-methyl-cholanthrene (MC)-inducible mono-oxygenase which has a 448-nm absorption maximum in the reduced-CO difference spectrum. Ethoxyresorufin exhibited a type I binding spectrum with liver microsomes from MC-induced rats, but there was no clear interaction with microsomes from control or phenobarbital (PB)-induced rats. Maximum MC-induction of type I binding and de-ethylase activity coincided with the appearance of a cytochrome P-450 spectrum whose absorption maximum was shifted to 448 nm. Low concentrations of alpha-naphthoflavone (ANF) or benzo[a]pyrene (BP) inhibited the de-ethylation with liver microsomes of MC-treated rats (150 approximately 10(-9)M) but not those of control rats. A kinetic analysis of BP inhibition ...
Molecular pharmacology, 1994
Rate control in acetylcholinesterase (AChE) involves a single anionic site whose anionic center c... more Rate control in acetylcholinesterase (AChE) involves a single anionic site whose anionic center controls rate-related biochemical and conformational changes in the E (free enzyme) and EA (acylated enzyme) conformers. Change in conformer structure and biochemistry affect binding, acylation, and hydrolysis. It is significant that the anionic-esteratic intersite distance is not altered during conformer change as E is converted to EA. In this enzyme system, cationic acetylcholine and anionic AChE are true structural, functional, and biochemical counterparts. The anionic center in the E conformer lies at the bottom of a sterically restricted, hydrophobic cleft < 8 A wide at the top and > 3 A wide at the bottom, while the anionic center in the EA conformer is relatively open. It is characterized by a decrease in the relative binding of hydrophobic cations and by an ability to bind large organic cations. Binding of acetylcholine, H+, or organic cations at the anionic site controls k2...
Drug metabolism and disposition: the biological fate of chemicals
Liver microsomes from 3-methylcholanthrene-pretreated Long-Evans rats catalyzed the 2- and the 4-... more Liver microsomes from 3-methylcholanthrene-pretreated Long-Evans rats catalyzed the 2- and the 4-hydroxylation of biphenyl and the O-deethylation of ethoxyresorufin, sustained by either NADPH or cumene hydroperoxide. In contrast, the liver microsomes from corn oil- or phenobarbital-pretreated rats catalyzed the NADPH- or cumene hydroperoxide-sustained 4-hydroxylation of biphenyl, but the rates of 2-hydroxylation or ethoxyresorufin deethylation were negligible. A monooxygenase system reconstituted with partially purified NADPH-cytochrome c reductase and cytochrome P-448 catalyzed NADPH-supported biphenyl 2- and 4-hydroxylation and ethoxyresorufin deethylation. A monooxygenase system reconstituted with the reductase and cytochrome P-450 catalyzed NADPH-supported biphenyl 4-hydroxylation but exhibited negligible 2-hydroxylation or ethoxyresorufin deethylation activites. Solubilized cytochrome P-448 catalyzed biphenyl 2- and 4-hydroxylation and ethoxyresorufin deethylation sustained by ...
Toxicology, 1986
Five putative chitin synthesis inhibitors (CSI) were tested to determine if they inhibited nucleo... more Five putative chitin synthesis inhibitors (CSI) were tested to determine if they inhibited nucleoside incorporation into acid precipitable material in a cell line from Manduca sexta (L.). The results varied. Diflubenzuron (DFB) (100 pm) inhibited cytidine incorporation by 38%; EL-494 (100 pm) inhibited adenosine incorporation by 43%; Bay Sir 8514 (100 urn) inhibited uridine incorporation by 24%. Superdiflubenzuron (100 pm) was the worst inhibitor overall {18-22%) for the benzoylphenyl urea CSI. The triazine CSI, CGA 19255, was the best inhibitor tested with 60% inhibition for cytidine and 49% for adenosine incorporation into DNA and RNA. Examination of cells incubated with diflubenzuron by scanning electron microscopy revealed distinct external morphological changes. Transmission electron microscopy showed that crystalline structures accumulated in the cytoplasm of cells treated with DFB. The crystalline structures were assumed to be diflubenzuron and they persisted even after diflubenzuron was removed from the medium.
Life Sciences, 1979
ABSTRACT Cuticular development of larvae was examined by electron microscopy and comparisons were... more ABSTRACT Cuticular development of larvae was examined by electron microscopy and comparisons were made between larvae exposed to methoprene, isopropyl (E, E)-11-methoxy-3, 7, 11-trimethyl-2, 4-dodecadienoate, those treated with the fluorescent insect growth regulator, 5-[[[5-(dimethylamino)-1-naphthalenyl]-sulfonyl]amino]-1, 3-benzodioxole (DNSAB), and untreated larvae. Larvae of all three groups were routinely fixed at 24, 48, and 72 hr posttreatment. Thin sections of the sixth-abdominal segment, anal papillae, midgut tissue, and Malpighian tubules were examined for morphological variations from controls.
Journal of Insect Physiology, 1976
Postharvest Biology and Technology, 1995
Cucumber (Cucumb sufivus cv. Dasher 3) fruit were immersed in water at 25,38, or 42°C for 30 min ... more Cucumber (Cucumb sufivus cv. Dasher 3) fruit were immersed in water at 25,38, or 42°C for 30 min prior to storage at 12 (nonchilling) or 2S"C (chilling) for two weeks to determine the effects of these treatments on chilling-induced changes in electrolyte leakage, and COz, and ethylene evolution. Storage at 2S"C resulted in a significant increase in electrolyte leakage, which decreased significantly as immersion temperature increased. Chilled fruit had higher rates of CO2 production than did nonchilled fruit following transfer to 21"C, but there was no difference due to immersion temperature. Following transfer to 21"C, nonchilled fruit produced no detectable ethylene whereas chilled fruit produced significant amounts of ethylene. The amount of chilling-induced ethylene production decreased with increased temperature of immersion, and this difference persisted for at least 72 h after transfer to 21°C. The amount of l-aminocyclopropane-1-carboxylic acid (ACC) was significantly higher in chilled than in nonchilled fruit although the amount of ACC in chilled fruit decreased significantly as immersion temperature increased. Nonchilled fruit had significantly higher ACC oxidase activity than did chilled fruit at the time of transfer to 21"C, and ACC oxidase activity decreased as immersion temperature increased.
Journal of Medical Entomology, 1984
... Another key step in the digestive process of he-matophagous insects is the lysis of the eryth... more ... Another key step in the digestive process of he-matophagous insects is the lysis of the erythrocytes. ... More recently the mechanism of midgut hemolysis of the stable fly was characterized by Spates et al. (1982). In the present study the hemolysin of the horn fly is investigated. ...
Toxicology, 1984
Diflubenzuron (DFB) significantly inhibited the uptake of uridine, adenosine, and cytidine but no... more Diflubenzuron (DFB) significantly inhibited the uptake of uridine, adenosine, and cytidine but not thymidine, in cultured Harding-Passey melanoma cells. Inhibition of nucleoside uptake was rapid (i.e., <_ 5 min) and could not be reversed by washing. These results suggest that DFB may affect membrane properties and-as shown by in vivo tests-growth of melanoma cells.
Archives of Biochemistry and Biophysics, 1987
Biochemistry, 1972
1-(5-Dimethylaminonaphthalene-1-sulfonamide)-3-N,N-dimethylaminopropane and 1-(5-dimethylarninona... more 1-(5-Dimethylaminonaphthalene-1-sulfonamide)-3-N,N-dimethylaminopropane and 1-(5-dimethylarninonaphthalene-1-sulfonamido)propane-3-trimethylammonium iodide are active-site-directed, equilibrium fluorescent probes. They are competitive inhibitors of horse serum cholinesterase (3.1.1.8). The basic group in each probe molecule binds at the anionic site. Subsequent binding of the fluorescent moiety is directed to an adjacent, hydrophobic site. Equilibrium dynamics of interaction of the probe-enzyme complexes were
Mutation Research Letters, 1985
1. Mutat Res. 1985 Mar;142(3):127-31. Measurement of cytochrome P-450 dependent dealkylation of a... more 1. Mutat Res. 1985 Mar;142(3):127-31. Measurement of cytochrome P-450 dependent dealkylation of alkoxyphenoxazones in hepatic S9s and hepatocyte homogenates: effects of dicumarol. Lubet RA, Nims RW, Mayer RT, Cameron JW, Schechtman LM. ...
Journal of Microscopy, 1974
The construction of a microspectrofluorometer with automatic correction capabilities is given. Th... more The construction of a microspectrofluorometer with automatic correction capabilities is given. The instrument uses a quantum counting system for correction of excitation spectra and an interpolating function generator for correction of emission spectra. An inexpensive analogue computer is an integral part of the electronic portion of the instrument and allows a number of mathematical manipulations to be performed on the sample and reference signals prior to recording or display. Under the conditions stated, the sensitivity of the instrument is in the 10−9 M range for quinine sulphate irradiated at 365 nm. The linear response range for quinine sulphate is 10−3 to 10−9 M. The operational wavelength range of the machine is between 226 and 700 nm.
Environmental Entomology, 2002
The biological effects of a commercially available neem seed extract (Neemix. 4.5, 4.5% azadirach... more The biological effects of a commercially available neem seed extract (Neemix. 4.5, 4.5% azadirachtin, AZ) were assessed on the brown citrus aphid, Toxoptera citricida (Kirklady), a recently introduced insect pest of citrus in the United States and its parasitoid, Lysiphlebus testaceipes. When small citrus seedlings were dipped with the neem extract at 11Ð180 ppm AZ, 0 Ð 8% of nymphs and 0 Ð17.5% of adults survived 7 d after the treatment while 95% of nymphs and 42.5% of adults in the control survived for the same period. The extract drastically reduced longevity of both adults and nymphs, adult fecundity, and molting of nymphs at all tested concentrations. Spraying neem extract (11Ð180 ppm AZ) onto potted citrus plants in the greenhouse also signiÞcantly reduced aphids by 20 Ð100%, while control aphid populations increased by 950% 7 d after treatment. Application of the extract had little impact on the survival of adult parasitoids and developing parasitoids within aphids because parasite emergences were similar between treated and untreated parasitized aphids. These results indicate that neem extract may be compatible with integrated pest management programs in citrus and should be evaluated for Þeld efÞcacy.
British Journal of Clinical Pharmacology, 1992
The O-dealkylation of seven 7-alkoxyquinoline derivatives by human hepatic and placental microsom... more The O-dealkylation of seven 7-alkoxyquinoline derivatives by human hepatic and placental microsomes and the effect of maternal cigarette smoking on placental 7alkoxyquinoline metabolism was studied. 2 None of several monoclonal antibodies to isoenzymes of cytochrome P450 had a clear effect on metabolism of the compounds by liver microsomes. 3 Maternal cigarette smoking induced the O-dealkylation of all of the 7-alkoxyquinoline derivatives, being greatest for 7-butoxyand 7-benzyloxyquinoline. 4 Placental 7-alkoxyquinoline metabolism induced by smoking was partially inhibited by the monoclonal antibody 1-7-1 raised against 3-methylcholanthrene-induced rat liver P450. 5 None of the 7-alkoxyquinoline O-dealkylations could be assigned specifically to any known P450 isoenzyme in human liver or placenta.
Analytical Biochemistry, 1992
A quantitative fluorometric assay for chitosanase activity in bacterial and plant tissues was dev... more A quantitative fluorometric assay for chitosanase activity in bacterial and plant tissues was developed. The assay can be conducted with either finely milled preparations of chitosan in suspension or dissolved chitosan; activity is based on measurements of glucosamine (GlcN) or oligomers of GlcN. GlcN is detected fluorometrically after reaction with fluorescamine with detection in the nanomole range. Fluorescence measurements of chitosanase activity and radioassay of chitinase in commercial preparations of chitinase from Streptomyces griseus revealed that both activities were present. Specific activities for the S. griseus chitosanase using suspended and soluble chitosans were respectively 1.24 and 6.4 mumol GlcN.min-1.mg protein-1. Specific activity of the S. griseus chitinase was 0.98 mumol GlcN.min-1.mg protein-1. Sweet orange callus tissue was tested for chitosanase and chitinase activity. It was necessary to remove small amine-containing molecules from the callus preparations before chitosanase activity could be assayed. The specific activity for chitinase and chitosanase in desalted extracts of nonembryogenic Valencia sweet orange callus tissue was determined to be 18.6 and 89.4 nmol GlcN.min-1.mg protein-1, respectively.
Biochemical Journal, 1986
The properties of five structurally related forms of cytochrome P-450 (PB1a, PB1b, PB2a, PB2b and... more The properties of five structurally related forms of cytochrome P-450 (PB1a, PB1b, PB2a, PB2b and PB2d) isolated from rats treated with phenobarbital have been compared with two forms isolated previously now termed ‘PB1c’ and ‘PB2c’ These enzymes were characterized by their marginal inducibility by phenobarbital and are clearly distinguishable from the major phenobarbital-inducible proteins. PB1a and PB1b differed in Mr (52,700 and 52,900), absorption spectra and papain-proteolysis fragments. However, they had identical N-terminal sequences. PB2a, PB2b and PB2d had apparent Mr values of 52,900, 52,900 and 50,800. PB2a and PB2b had different N-terminal sequences and, after digestion with papain, gave different papain-proteolysis fragments. The N-terminal sequence of PB2b was similar to, but not identical with, that of pregnenolone-16 alpha-carbonitrile-inducible P-450 species, and PB2b was the protein most closely related to PB2c. The extent of immunocross-reactivity among the forms ...
Journal of Polymer Science Part A-1: Polymer Chemistry, 1970
ABSTRACT Fluorescent probes which are active-site-directed, reversible, competitive inhibitors of... more ABSTRACT Fluorescent probes which are active-site-directed, reversible, competitive inhibitors of serum cholinesterase (ChE) enzymes have been designed and synthesized. Reversible inhibitors of enzyme active sites have a unique importance when they act as fluorescent probes, allowing fluorescence spectroscopic detection of conformation changes and activesite dynamics. 5-Dimethylamino-naphthalene-1-sulfonamido-N,N-dimethyl-n-propyl-amine and its aliphatic quaternary derivative are fluorescent probes for serum cholinesterase. The quaternary probe forms complexes with acetylcholinesterase (AChE). The dissociation constants Kd for the two probes with serum ChE are 6.0 × 10−7 and 6.5 × 10−7M. The inhibition constants Ki are 3.1 × 10−6 and 6.3 × 10−6M from the slopes of Lineweaver-Burk plots. The Michelis constant Km for the enzyme was 8.8 × 10−4M.
Methods in Enzymology, 1978
Publisher Summary This chapter focuses on the direct fluorometric methods for measuring mixed-fun... more Publisher Summary This chapter focuses on the direct fluorometric methods for measuring mixed-function oxidase activity. Ullrich and Weber developed a direct fluorometric method to measure the mouse liver microsomal cytochrome-P-450-dependent O-dealkylation of 7-ethoxycoumarin to yield 7-hydroxycoumarin. Recently, Burke and Mayer described a direct fluorometric assay to measure the O-dealkylation of ethoxyresorufin. The broad substrate specificity and ready induction of the monooxygenase has allowed the development of a large number of specific assays for the enzyme system. Many of the methods require solvent extraction of metabolites and subsequent analysis to quantitate the concentration of the metabolite. The number of manipulations required in these assay methods and the problems involved in solvent extraction of compounds of intermediate polarity complicates and extends the time required for analysis of enzyme activity. Several direct spectrophotometric and spectrophotofluorimetric assays are developed to obviate these problems, and two fluorescent assays are encapsulated in this chapter.
Drug metabolism and disposition: the biological fate of chemicals
Page 1. Send reprint requests to: Dr. MD Burke. Biochemistry Department. The University of Texas ... more Page 1. Send reprint requests to: Dr. MD Burke. Biochemistry Department. The University of Texas Health Science Center. 5323 Harry Hines Blvd.. Dallas, Texas 75235 583 DRUG METABOLISM AND DIsPosITIoN Copyright ...
Drug metabolism and disposition: the biological fate of chemicals
Certain characteristics of ethoxyresorufin O-de-ethylation, as catalyzed by microsomes of liver, ... more Certain characteristics of ethoxyresorufin O-de-ethylation, as catalyzed by microsomes of liver, lung, and intestine of control and pretreated rats and hamsters, were studied. The results support previous suggestions that the reaction is catalyzed primarily by a 3-methyl-cholanthrene (MC)-inducible mono-oxygenase which has a 448-nm absorption maximum in the reduced-CO difference spectrum. Ethoxyresorufin exhibited a type I binding spectrum with liver microsomes from MC-induced rats, but there was no clear interaction with microsomes from control or phenobarbital (PB)-induced rats. Maximum MC-induction of type I binding and de-ethylase activity coincided with the appearance of a cytochrome P-450 spectrum whose absorption maximum was shifted to 448 nm. Low concentrations of alpha-naphthoflavone (ANF) or benzo[a]pyrene (BP) inhibited the de-ethylation with liver microsomes of MC-treated rats (150 approximately 10(-9)M) but not those of control rats. A kinetic analysis of BP inhibition ...
Molecular pharmacology, 1994
Rate control in acetylcholinesterase (AChE) involves a single anionic site whose anionic center c... more Rate control in acetylcholinesterase (AChE) involves a single anionic site whose anionic center controls rate-related biochemical and conformational changes in the E (free enzyme) and EA (acylated enzyme) conformers. Change in conformer structure and biochemistry affect binding, acylation, and hydrolysis. It is significant that the anionic-esteratic intersite distance is not altered during conformer change as E is converted to EA. In this enzyme system, cationic acetylcholine and anionic AChE are true structural, functional, and biochemical counterparts. The anionic center in the E conformer lies at the bottom of a sterically restricted, hydrophobic cleft < 8 A wide at the top and > 3 A wide at the bottom, while the anionic center in the EA conformer is relatively open. It is characterized by a decrease in the relative binding of hydrophobic cations and by an ability to bind large organic cations. Binding of acetylcholine, H+, or organic cations at the anionic site controls k2...
Drug metabolism and disposition: the biological fate of chemicals
Liver microsomes from 3-methylcholanthrene-pretreated Long-Evans rats catalyzed the 2- and the 4-... more Liver microsomes from 3-methylcholanthrene-pretreated Long-Evans rats catalyzed the 2- and the 4-hydroxylation of biphenyl and the O-deethylation of ethoxyresorufin, sustained by either NADPH or cumene hydroperoxide. In contrast, the liver microsomes from corn oil- or phenobarbital-pretreated rats catalyzed the NADPH- or cumene hydroperoxide-sustained 4-hydroxylation of biphenyl, but the rates of 2-hydroxylation or ethoxyresorufin deethylation were negligible. A monooxygenase system reconstituted with partially purified NADPH-cytochrome c reductase and cytochrome P-448 catalyzed NADPH-supported biphenyl 2- and 4-hydroxylation and ethoxyresorufin deethylation. A monooxygenase system reconstituted with the reductase and cytochrome P-450 catalyzed NADPH-supported biphenyl 4-hydroxylation but exhibited negligible 2-hydroxylation or ethoxyresorufin deethylation activites. Solubilized cytochrome P-448 catalyzed biphenyl 2- and 4-hydroxylation and ethoxyresorufin deethylation sustained by ...
Toxicology, 1986
Five putative chitin synthesis inhibitors (CSI) were tested to determine if they inhibited nucleo... more Five putative chitin synthesis inhibitors (CSI) were tested to determine if they inhibited nucleoside incorporation into acid precipitable material in a cell line from Manduca sexta (L.). The results varied. Diflubenzuron (DFB) (100 pm) inhibited cytidine incorporation by 38%; EL-494 (100 pm) inhibited adenosine incorporation by 43%; Bay Sir 8514 (100 urn) inhibited uridine incorporation by 24%. Superdiflubenzuron (100 pm) was the worst inhibitor overall {18-22%) for the benzoylphenyl urea CSI. The triazine CSI, CGA 19255, was the best inhibitor tested with 60% inhibition for cytidine and 49% for adenosine incorporation into DNA and RNA. Examination of cells incubated with diflubenzuron by scanning electron microscopy revealed distinct external morphological changes. Transmission electron microscopy showed that crystalline structures accumulated in the cytoplasm of cells treated with DFB. The crystalline structures were assumed to be diflubenzuron and they persisted even after diflubenzuron was removed from the medium.
Life Sciences, 1979
ABSTRACT Cuticular development of larvae was examined by electron microscopy and comparisons were... more ABSTRACT Cuticular development of larvae was examined by electron microscopy and comparisons were made between larvae exposed to methoprene, isopropyl (E, E)-11-methoxy-3, 7, 11-trimethyl-2, 4-dodecadienoate, those treated with the fluorescent insect growth regulator, 5-[[[5-(dimethylamino)-1-naphthalenyl]-sulfonyl]amino]-1, 3-benzodioxole (DNSAB), and untreated larvae. Larvae of all three groups were routinely fixed at 24, 48, and 72 hr posttreatment. Thin sections of the sixth-abdominal segment, anal papillae, midgut tissue, and Malpighian tubules were examined for morphological variations from controls.
Journal of Insect Physiology, 1976