Ricardo N Farías | Universidad Nacional de Tucumán (original) (raw)

Papers by Ricardo N Farías

Research article Linear array of conserved sequence motifs to discriminate protein subfamilies: s... more Research article Linear array of conserved sequence motifs to discriminate protein subfamilies: study on pyridine nucleotide-disulfide reductases

Journal of Bacteriology, 1972

The allosteric inhibition by sodium of the (Ca 2+ )-adenosine triphosphatase (EC 3.6.1.3) from Es... more The allosteric inhibition by sodium of the (Ca 2+ )-adenosine triphosphatase (EC 3.6.1.3) from Escherichia coli was found to be dependent on the lipid composition of the cell membrane.

Journal of Bacteriology, 1973

The allosteric properties of the membrane-bound (Ca 2+ )-adenosine triphosphatase of an unsaturat... more The allosteric properties of the membrane-bound (Ca 2+ )-adenosine triphosphatase of an unsaturated fatty acid auxotroph of Escherichia coli were studied in membranes with different fatty acid compositions. The Hill coefficient of the inhibition by Na + ranged from 1.4, in the case where the auxotroph was grown with cis -vaccenic acid as supplement, to 2.8 when grown on linolenic acid. The results indicate that no fatty acid is particularly involved in the allosteric phenomena. A correlation between the values of the Hill coefficient and the double bond index or the ratio of the double bond index saturated to the fatty acids of the membrane was found. These facts are interpreted as a modulation by the membrane fluidity of the allosteric behavior of the membrane-bound enzyme. The general biological character of this phenomenon is discussed in this paper.

Journal of General Microbiology, 1975

The effect of fatty acids on Escherichia coli K 1 2 was dependent on tbe source of the inoculum, ... more The effect of fatty acids on Escherichia coli K 1 2 was dependent on tbe source of the inoculum, the growth phase and the washing of the bacteria. The effects of saturated fatty acids from C4 to C16 and oleic acid at two concentrations (0.1 and 0.4 %, wlv) were determined on E. coli KI2/154 growing exponentially in five different culture media. Depending on the media, 0.1 % fatty acids increased the doubling times of the cultures by up to 96 %. Fatty acids of medium chain length (C6 to C I I) at 0.4 % produced a decrease in cell concentration, nonanoic and decanoic acids being the most effective. A correlation was found between the decrease in cell concentration and the loss of viability of the cultures after addition of 0.4 % decanoic acid, with stationary-phase bacteria being affected more than those from exponential-phase cultures. Experiments carried out with E. coli B and c gave results similar to those obtained with E. coli KI2/154.

Eur Biophys J Biophys Lett, 2009

The Journal of General and Applied Microbiology, 1979

Journal of Theoretical Biology, 1975

ABSTRACT

Journal of Agricultural and Food Chemistry, 1993

Biochemical Pharmacology, 1993

Biochimica et Biophysica Acta (BBA) - Biomembranes, 1978

Archives of Biochemistry and Biophysics, 1999

Previous results from our laboratory have shown that NADH-supported electron flow through the Esc... more Previous results from our laboratory have shown that NADH-supported electron flow through the Escherichia coli respiratory chain promotes the reduction of cupric ions to Cu(I), which mediates damage of the respiratory system by hydroperoxides. The aim of this work was to characterize the NADH-linked cupric reductase activity from the E. coli respiratory chain. We have used E. coli strains that either overexpress or are deficient in the NADH dehydrogenase-2 (NDH-2) to demonstrate that this membrane-bound protein catalyzes the electron transfer from NADH to Cu(II), but not to Fe(III). We also show that purified NDH-2 exhibits NADH-supported Cu(II) reductase activity in the presence of either FAD or quinone, but is unable to reduce Fe(III). The K m values for free Cu(II) were 32 ؎ 5 pM in the presence of saturating duroquinone and 22 ؎ 2 pM in the presence of saturating FAD. The K m values for NADH were 6.9 ؎ 1.5 M and 6.1 ؎ 0.7 M in the presence of duroquinone and FAD, respectively. The quinone-dependent Cu(II) reduction occurred through both O 2 •؊-mediated and O 2 •؊-independent pathways, as evidenced by the partial inhibitory effect (30-50%) of superoxide dismutase, by the reaction stoichiometry, and by the enzyme turnover numbers for NADH and Cu(II). The cupric reductase activity of NDH-2 was dependent on thiol groups which were accessible to p-chloromercuribenzoate at low, but not at high, ionic strength of the medium, a fact apparently connected to a conformational change of the protein. To our knowledge, this is the first protein with cupric reductase activity to be isolated and characterized in its biochemical properties.

Analytical Biochemistry, 2002

In this paper we report the up to now ignored fluorescence properties of the specific Cu(I)-chela... more In this paper we report the up to now ignored fluorescence properties of the specific Cu(I)-chelator bathocuproine disulfonate and their application in assays of total copper and Cu(I). The method is based on the linear quenching of the bathocuproine disulfonate emission at 770 nm (k ex 580 nm) by increasing concentrations of Cu(I), at pH 7.5. Copper concentrations as low as 0:1 lM can be determined. Other metal ions (iron, manganese, zinc, cadmium, cobalt, nickel) do not interfere. The procedure for total copper determination in proteins includes HCl treatment to release the copper, neutralization to pH 7.5 in the presence of citrate to stabilize the copper, and reduction of the copper to Cu(I) by ascorbate in the presence of the chelator. This assay gave results coincident with the analysis by atomic absorption spectroscopy in two selected proteins. In addition, conditions are described (omitting HCl treatment and reduction by ascorbate) for direct measurement of Cu(I) in native proteins, as illustrated for the Escherichia coli NADH dehydrogenase-2. Data show that the fluorometric assays described in this paper are simple and convenient procedures for total copper and direct Cu(I) quantification in determined biological samples.

Journal of Cellular Physiology, 2011

Thyroid hormones (THs) exert a broad range of actions on development, growth, and cell differenti... more Thyroid hormones (THs) exert a broad range of actions on development, growth, and cell differentiation by both genomic and nongenomic mechanisms. THs regulate lymphocyte function, but the participation of nongenomic actions is still unknown. Here the contribution of both genomic and nongenomic effects on TH-induced division of T cells was studied by using free and noncell permeable THs coupled to agarose (TH-ag). THs-ag led to cell division, but to a lesser extent than free hormones. THs induced nongenomically the rapid translocation of protein kinase C (PKC) ζ isoform to cell membranes, extracellular-signal-regulated kinases (ERK1/2) phosphorylation and nuclear factor-κB (NF-κB) activation. The signaling cascade include sphingomyelinases acting up-stream the activation of PKCζ isoform, while ERK and NF-κB are activated downstream this PKC isoenzyme. Both free and THs-ag increased the protein and mRNA levels of TH nuclear receptor TRα1, while only free hormones incremented the inducible NOS gene and protein levels as well as a calcium independent NOS activity. Both effects were blunted by PKCζ inhibition. These results indicate that THs, by triggering a nongenomic signaling cascade that involves Smases-mediated activation of PKCζ, lead to ERK 1/2 and NF-κB activation and to the genomic increase of TRs and the inducible nitric oxide synthase protein and mRNA levels, improving T lymphocyte proliferation. These finding not only contribute to the understanding of the mechanisms involved in TH modulation of lymphocyte physiology, but would also point out for the first time the interplay between genomic and nongenomic TH actions in T cells.

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Journal of Biological Chemistry, 1972

Journal of Biological Chemistry, 1986

We have studied, by fluorescence methods, the association of insulin to liposomes, the modificati... more We have studied, by fluorescence methods, the association of insulin to liposomes, the modification of lipid fluidity, and the fusion of vesicles induced by insulin. All parameters showed a similar dependence on pH and ionic strength of the medium and on negative charges in liposomes. The influence of temperature indicated that the association of insulin to liposomes per se was not sufficient to produce a decrease in lipid fluidity and fusion of liposomes. The modification of lipid fluidity induced by insulin in biological membranes is discussed as a possible general event in the action of the hormone.

Journal of Biological Chemistry, 1993

Similar cold-sensitive properties, values of dissociation constants (Kd = 1 X 10"' M), and regula... more Similar cold-sensitive properties, values of dissociation constants (Kd = 1 X 10"' M), and regulatory effectors were found for the cold-sensitive cytosolic 3,6,3'-triiodo-~-thyronine (L-T3)-binding protein (CTBP) and pyruvate kinase from human erythrocyte. Various metabolites of the blood cell were assayed for their effects on CTBP activity after heat and cold preincubation treatments. Among these compounds, five-and six-carbon phosphorylated sugars were effective in protecting the CTBP activity against cold inactivation, whereas only ATP and dATP blocked activation by heat treatments. The effects of fructose 1,6-bisphosphate, fructose 2,6-bisphosphate, and ATP were obtained at physiological concentrations. Threecarbon phosphorylated intermediates of glycolysis, ADP, AMP, CAMP, and GTP had no effect on cold and heat treatments. The monomer-tetramer interconversion of the enzyme was also regulated by fructose 1,6bisphosphate and ATP. The association is under the control of fructose 1,6-bisphosphate, whereas the dissociation is under ATP control. This regulation may have physiological relevance since the hormone binds to the tetrameric form of the enzyme at a site other than the active site. Pyruvate kinase (PK'; ATP:pyruvate O'-phosphotransferase, EC 2.7.1.40) is glycolytic enzyme which consist of four identical subunits of about 60 kDa. There are four distinct isozymes, being each primarily endogenous to a certain tissue type: liver (L), erythrocyte (R), skeletal muscle (M1), and kidney (M,) (1). The Land R-type and M1-and M2-type

Molecular and Cellular Biochemistry, 1981

Cytosolic adenylate cyclase activity from rat seminiferous tubules was purified by chromtography ... more Cytosolic adenylate cyclase activity from rat seminiferous tubules was purified by chromtography in DEAE-cellulose, hydroxylapatite and Bio-Gel A-0.5 m as well as by centrifugation in sucrose gradients. In all these purification steps, fractions with adenylate cyclase activity also contained binding activity for L-T3. Binding studies indicate the existence of two L-T3 receptor components associated to adenylate cyclase activity. The component exhibiting the highest hormone affinity has the lowest binding capacity.

Journal of Raman Spectroscopy, 2004

... DOI: 10.1002/jrs.1239 Comparative vibrational analysis of thyronine hormones using infrared a... more ... DOI: 10.1002/jrs.1239 Comparative vibrational analysis of thyronine hormones using infrared and Raman spectroscopy and density functional theory calculations Rosa MS ´Alvarez,1 Ricardo N. Farıas1 and Peter Hildebrandt2∗ ...

Journal of Membrane Biology, 2003

The surface balance technique was employed to study the interactions of 3,5,3¢,5¢ tetraiodo L-thy... more The surface balance technique was employed to study the interactions of 3,5,3¢,5¢ tetraiodo L-thyronine, 3,5,3¢ triiodo L-thyronine, and 3,5-diiodothyronine with monomolecular phospholipid monolayers spread at the air-water interface. With this technique the insertion of thyroid hormones into egg yolk phosphatidylcholine was investigated. An increase of surface pressure and a substantial decrement in surface potential were observed after the injection of these hormones beneath a phospholipid monolayer. The negative dipole contribution upon hormone interaction opposes the well-known positive contribution of phospholipids. These effects correlated with iodo content of the thyroid molecule analogues 3,5,3¢,5¢ tetraiodo L-thyronine >3,5,3¢ triiodo L-thyronine >3,5-diiodothyronine. To our knowledge, these observations suggest a new and surprising effect of thyroid hormones on the regulation of transmembrane dipolar organization.