Pradeep Kumar - Academia.edu (original) (raw)

Papers by Pradeep Kumar

Biochem Biophys Res Commun, 2004

Asian journal of andrology, 1999

Capacitation and acrosome reaction are important prerequisites of the fertilization process. Capa... more Capacitation and acrosome reaction are important prerequisites of the fertilization process. Capacitation is a highly complex phenomenon occurring in the female genital tract, rendering the spermatozoa capable of binding and fusion with the oocyte. During capacitation various biochemical and biophysical changes occur in the spermatozoa and the spermatozoal membranes. Ions and ion channels also play important roles in governing the process of capacitation by changing the fluxes of different ions which in turn controls various characteristics of capacitated spermatozoa. Along with the mobilization of ions the generation of free radicals and efflux of cholesterol also plays an important role in the capacitation state of the spermatozoa. The generation of free radical and efflux of cholesterol change the mechanodynamic properties of the membrane by oxidation of the polyunsaturated lipids and by generating the cholesterol free patches. The process of capacitation renders the spermatozoa ...

Biochemistry and molecular biology international, 1993

Treatment of spermatozoa with 10 mM caffeine increases the rotational mobility of thiol-containin... more Treatment of spermatozoa with 10 mM caffeine increases the rotational mobility of thiol-containing proteins in a defined micellar micro-environment. This is associated with inhibition of superoxide dismutase activity and augmented superoxide anion radical generation. Increased sperm competence in presence of caffeine in human oligospermia is explained by these observations. Inhibition of cyclic phosphodiesterase by caffeine is suggested to be part of the observed lattice-rearrangement.

Biochemistry and molecular biology international, 1994

Flavin photochemistry involves the production of transient flavin free radicals which in turn sen... more Flavin photochemistry involves the production of transient flavin free radicals which in turn sensitize molecular oxygen to generate superoxide. The blue light induced photochemical chain reaction of flavins may be blocked at two different levels by photoresponse inhibitors. A protein-bound/lipid-bound flavin located on the biomembrane may take part in the blue-light mediated sensory transduction by 'releasing' a 'free radical messenger' equivalent into the cell interior.

Urologia Internationalis, 2001

Background: Contractile activity of the muscular coat of the epididymis wall is considered the ma... more Background: Contractile activity of the muscular coat of the epididymis wall is considered the major driving force for the propulsion of sperm through the male reproductive tract. Methods: Region-specific changes in the status of membrane thiols and the free radical scavening potential of the male reproductive tract of the rat were observed. Results: The present study shows that the local biochemical milieu has some influence on the transport of spermatozoa through the male reproductive tract. The vas deferens showed a higher level of superoxide dismutase activity and a low profile of thiol exposure. Conclusion: We conclude that the strong scavenging potential and the lesser thiol exposure of the vas create an apparently inert vas lumen which facilitates the transit of spermatozoa through the vas.

Systems Biology in Reproductive Medicine, 1997

Sperm is highly sensitive to superoxide radical surge in the granuloma interior. To investigate p... more Sperm is highly sensitive to superoxide radical surge in the granuloma interior. To investigate possibility of a superoxide radical bomb, the role of an oxyradical on the spermatozoon was studied in vitro using potassium superoxide, a potent superoxide radical producer. Results confirm that the superoxide radical has a unique site-specific scissoring power.

Archives of Andrology, 1997

ABSTRACT Even though the aminopeptidase and amylase are the major liquefying factors in the lique... more ABSTRACT Even though the aminopeptidase and amylase are the major liquefying factors in the liquefaction process of the ejaculated semen-coagulum, the exact nature of "switching on" phenomena has not been elucidated yet. Monitoring the rate of production of the asborbyl radical, an indirect method for oxyradical-stress measurement, this prima facie study reports the involvement of oxygen radical in the liquefaction process of coagulated semen.

Life Sciences, 2000

NADPH dependent O2- production in the ovary and uterus of cycling and pregnant mice was estimated... more NADPH dependent O2- production in the ovary and uterus of cycling and pregnant mice was estimated employing a novel technique of time-lapse electron spin resonance enhancement of a superoxide-trapping spin trap. The NADPH dependent O2- generation in the mouse ovary increased during the early pre-ovulatory phase in cycling females and during extended luteal phase in pregnant animals. A peak of uterine NADPH dependent O2- production at proestrous in the cycling animals at pre-implantation phase in pregnant animals suggested a contribution of this enzyme towards generating high levels of superoxide anion radical during the respective stages. Both ovarian and uterine NADPH dependent O2- production appeared to be LH-inducible.

Journal of Biological Chemistry, 2001

Journal of Biological Chemistry, 2003

IUBMB Life, 1998

The primary aim of this study was to evaluate the effect of melatonin on the oxyradical load in a... more The primary aim of this study was to evaluate the effect of melatonin on the oxyradical load in avian thyroid. The superoxide free radicals have been spin trapped by EPR spectroscopy in the thyroid gland of Indian rock pigeon Co/umba/ivia following melatonin implantation for two weeks. Melatonin implantation resulted in augmentation in the levels of superoxde radical in the thyroid gland of pigeons with a concomitant decrease in the levels of the total superoxide dismutase activity. This was also associated with increased lipid peroxidation. Melatonin implantation caused a significant increase in plasma levels of glucose. Plasma levels of thyroxine (T4) and triiodothyronine (T3) were lower in the melatonin-treated pigeons. However, the T3/T4 ratio was higher following melatonin implantation. Since iodination of tyrosine is an H2Oz-dependent phenomenon, the inhibition in the activity of SOD could lead to impaired thyroid hormone synthesis.

International Journal of Andrology, 2001

Spermatic granulomas are believed to maintain`physiological harmony' in the male reproductive tra... more Spermatic granulomas are believed to maintain`physiological harmony' in the male reproductive tract by maintaining a balance of hydrostatic pressure post-vasectomy. The mechanism for the disposal of deposited spermatozoa in the granuloma core is not clear. A fourfold rise in the production of superoxide along with ascorbyl and dienyl radicals and a 50% drop in the production of nitric oxide (NO) radicals by granuloma tissue hints that a reaction between NO and superoxide radicals could lead to the formation of peroxynitrite species which may contribute to the disposal of spermatozoa in the granuloma core. A higher protease activity and low hypoxanthine content in the granuloma indicates that a free radical driven sperm disposal system is active in granulomas.

FEBS Letters, 1991

Thi~ .~tudy report~ that administration of TStl in young female mice rc~tllt,~ in a coneomitt~mt ... more Thi~ .~tudy report~ that administration of TStl in young female mice rc~tllt,~ in a coneomitt~mt ~tugment~ttion of SOD activity in d~e thyroid 81and, A stron~ thyroid adrenal interdcl'~ndence wa~ "-lisp evident in the form or a marked Idiot of SOD activity, ~n the adrenal ~land in r©~p~n~e Io TSH administration. Ver~ recently SOD/O,~ sy~tent had bean identified ¢,s a potent Io!=O= i/,enerator which provides suh~tr=Lte for the action of key enzyme in thyroxine and progesterone biosynthesis, vi~,, the p~roxida~e, Titus, these result~ strongly sui/,gcst that trophic hormon¢~ tonically stimul~tte hof mone bio~ynthesi~ by moduhttinli! =tetivalion/,~uppression at'specific enzyme~, whi;h could be the basi~ of the tuning secluenee.

Diabetes, 2006

A point mutation in the Stat5b DNA binding domain in the nonobese diabetic (NOD) mouse was shown ... more A point mutation in the Stat5b DNA binding domain in the nonobese diabetic (NOD) mouse was shown to have weaker DNA binding compared with the B6 Stat5b. Here, we assessed the binding ability of the mutant Stat5b in the B6 genetic background (B6.NOD-c11) and the wild-type Stat5b in the NOD background (NOD.Lc11). To our surprise, the binding ability of Stat5b is inconsistent with the presence or absence of the Stat5b mutation in these congenic mice but is correlated with the expression levels of the Crkl protein, which was coprecipitated by an anti-Stat5b antibody. Both the expression of Crkl and the Stat5b binding ability are the highest in B6.NOD-c11 and the lowest in NOD while intermediate in B6 and NOD.Lc11 mice. We demonstrated that the adapter molecule Crkl can bind Stat5b and that the Crkl protein is a Stat5b binding cofactor. More importantly, profection of Crkl recombinant protein significantly increased Stat5b binding ability and rescued the binding defect of the NOD mutant ...

Clinica Chimica Acta, 1994

Biochemical and Biophysical Research Communications, 1993

Vasectomy induces an immediate biophysical incompetence in epididymal spermatozoa in terms of the... more Vasectomy induces an immediate biophysical incompetence in epididymal spermatozoa in terms of the erroneous execution of membrane configuration processes, premature membrane melting and untimely protein gyration. Disturbances in the planned expression 'foreign proteins' and the possible 'swinging off' of these molecules from the membrane crystals might tease the immune system and might deprive the spermatozoa of the essential recognizing terminals.

Biochemical and Biophysical Research Communications, 1994

Biochemical and Biophysical Research Communications, 1991

In the absence ~ its substrate hydrogen peroxide, peroxidase exhibits perturbations in its Fe~-he... more In the absence ~ its substrate hydrogen peroxide, peroxidase exhibits perturbations in its Fe~-heme center, when incubated with ascorbic acid. The electron paramagnetic pattern sprang towards a higher g-value side, denoting a sharpening of the rhombic axial symmetry around the heme-center. The interpretation is ~at the ascorbate dependent peroxidase action starts with the formation of an Fe ~-ascorbate charge transfer complex intermediate.

Biochemical and Biophysical Research Communications, 2004

Capacitated mammalian spermatozoa undergo a fusion response of their head plasma membrane and the... more Capacitated mammalian spermatozoa undergo a fusion response of their head plasma membrane and the outer acrosomal membrane leading to vesiculation classically known as acrosome reaction. Acrosome reaction occurs in response to various acrosome reaction inducers including zona pellucida proteins, calcium ionophore, dibutyryl cAMP, progesterone, etc. All the acrosome reaction inducers cause a transient of calcium influx into the sperm through voltage-dependent cation channels. Efflux of chloride, stimulation of activity of phospholipases, and phosphorylation of proteins are other known changes introduced by acrosome reaction inducers. Macromolecular organization and dynamics of sperm membranes during the progression of this vesiculation are largely unexplored. In this study, we report that progesterone induced the formation of horizontal microdomains within the exofacial surfaces of sperm membranes, which showed progressive and independent alterations in molecular dynamics. In the light of this observation, we propose that sperm membrane rafts may contain both horizontal and vertical microdomains.