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Biomedical subjects

R K Tripathi

Publications and source records attributed to R K Tripathi.

70 records · Page 4Linked to original sources
PubMed1979

Properties and affinity purification of the mixed-type putative acetylcholine receptor from wild and a mutant strain of hose flies.

Binding of decamethonium to a soluble preparation from house fly head (either wild or a mutant strain) showed a single kind of binding with values for wild strain of Kd = 0.095 micrometers and Bmax = 0.22 nmol/mg protein. The mutant had a four-fold greater affinity and a seven-fold lesser amount. The binding was blocked by both nicotinic and muscarinic drugs. The decamethonium binding migrated in sucrose gradients as a single peak, with sedimentation coefficient s20,w = 12.5 S and therefore a molecular weight of 342 000. Purification by affinity chromatography was achieved with only partial loss of activity, andthe purified material demonstrated a single band on analytical disc gel electrophoresis. Electrophoresis in sodium dodecyl sulphate gels showed two subunits of molecular wegiths 94 000 and 64 000. Both subunits had an isoelectric point of 4.8.

Animals↗
PubMed1978

Substrate preferences of wild and a mutant house fly acetylcholinesterase and a comparison with the bovine erythrocyte enzyme.

Comparisons were made of purified acetylcholinesterase from the heads of wild type house flies with a mutant form (which bound organophosphates and carbamates less tightly). Using 12 substrates and 6 quaternary inhibitors, the only substantial difference was that the Km for butyrylcholine was 25 times greater for the mutant enzyme, suggesting that butyrylcholine and the organophosphates and carbamates shared a common binding site. The pure enzyme from the wild type house fly was also compared with bovine erythrocyte acetylcholinesterase. The major difference was again with butyrylcholine as substrate: the ability to acylate or deacylate was 30 times greater in the fly enzyme (the Km values differed by a factor of 4).

Acetylcholinesterase↗
PubMed1978

Molecular and structural characteristics of house fly brain acetylcholinesterase.

Acetylcholinesterase (acetylcholine hydrolase, EC 3.1.1.7) from the brains of house flies (Musca domestica L., tetrachlorvinphos-resistant strain) was examined for molecular and structural features, including molecular weight, Stokes radii, partial specific volumes, sedimentation coefficients and frictional ratios. Acetylcholinesterase purified by affininity chromatography was examined in the electron microscope by negative staining and three molecular forms were clearly observed (monomers, dimers and tetramers). Several tetrameric configurations were observed as well as structures of similar size showing tails. In the preparations of acetylcholinesterase so far examined, no globular structures having more than four monomeric units were observed.

Acetylcholinesterase↗
PubMed1978

Biochemical genetics of altered acetylcholinesterase resistance to insecticides in the house fly.

Resistance to the organophosphate insecticide tetrachlorvinphos was examined in a house fly (Musca domestica L.) strain with an altered acetylcholinesterase (AChE) of decreased sensitivity to inhibition by the insecticide. Genetic tests showed that both resistance and the altered AChE were controlled by semi-dominant gene(s) on chromosome II. The gene for resistance was five crossover units from the mutant marker stubby wing (stw). A house fly strain was prepared in which resistance was introduced in to a susceptible stw strain by recombination. Biochemical assays revealed that the altered AChE was introduced along with resistance. Assays of the AChE of resistant and susceptible stw strains by two independent methods showed that the enzyme from resistant flies was 30 times more slowly inhibited by tetrachlorvinphos than the enzyme from susceptible flies.

Acetylcholinesterase↗
PubMed1977

Purification of acetylcholinesterase from house fly brain by affinity chromatography.

Acetylcholinesterase (acetylcholine hydrolase, EC 3.1.1.7) from the heads of house flies (Musca domestica L.) was purified by affinity chromatography. The enzyme was adsorbed from the crude extracts on an affinity column containing trimethyl(p-aminophenyl) ammonium chloride hydrochloride (Ki approximately 1.7 - 10(-4) M), covalently linked to Sepharose 4B, then eluted with a solution of a selective reversible inhibitor, 1,5-bis (4-allyl dimethyl ammoniumphenyl)-pentan-3-one dibromide (BW 284C51; Ki approximately 1 - 10(-7) M). The enzyme was purified 1223 times in one step and had a specific activity of 752 units/mg protein. Disc gel electrophoresis in polyacrylamide gel revealed five protein bands, four corresponding to the enzyme activity bands and one devoid of enzyme activity. On the basis of periodic acid-Schiff stain intensity, the slower moving isozyme I and the contaminating band appear to be rich in carbohydrate. The purity of the enzyme estimated by disc gel electrophoresis was 94%. Density gradient centrifugation in sucrose showed two major species each of which ran as a single band on disc gel electrophoresis. The average molecular weights were 306000 (+/- 11 150) for heavy (s20,w = 11.5 S) form and 143000 (+/- 4700) for light (s20,w = 6.9 S) form.

Acetylcholinesterase↗
PubMed1969

Mechanism of action of the antifungal antibiotic pyrrolnitrin.

Pyrrolnitrin at 10 mug/ml inhibited the growth of Saccharomyces cerevisiae, Penicillium atrovenetum, and P. oxalicum. The primary site of action of pyrrolnitrin on S. cerevisiae was the terminal electron transport system between succinate or reduced nicotinamide adenine dinucleotide (NADH) and coenzyme Q. At growth inhibitory concentrations, pyrrolnitrin inhibited endogenous and exogenous respiration immediately after its addition to the system. In mitochondrial preparations, the antibiotic inhibited succinate oxidase, NADH oxidase, succinate-cytochrome c reductase, NADH-cytochrome c reductase, and succinate-coenzyme Q(6) reductase. In addition, pyrrolnitrin inhibited the antimycin-insensitive reduction of dichlorophenolindophenol and of the tetrazolium dye 2,2'-di-p-nitrophenyl-(3,3'-dimethoxy-4,4'-bi-phenylene)5,5'-diphenylditetrazolium. The reduction of another tetrazolium dye, 2-p-iodophenyl-3-p-nitrophenyl-5-phenyltetrazolium chloride, that was antimycin-sensitive, was also inhibited by pyrrolnitrin. The antibiotic had no effect on the activity of cytochrome oxidase, and it did not appear to bind with flavine adenine dinucleotide, the coenzyme of succinic dehydrogenase. In whole cells of S. cerevisiae, pyrrolnitrin inhibited the incorporation of (14)C-glucose into nucleic acids and proteins. It also inhibited the incorporation of (14)C-uracil, (3)H-thymidine, and (14)C-amino acids into ribonucleic acid, deoxyribonucleic acid, and protein, respectively. The in vitro protein synthesis in Rhizoctonia solani and Escherichia coli was not affected by pyrrolnitrin. Pyrrolnitrin also inhibited the uptake of radioactive tracers, but there was no general damage to the cell membranes that would result in an increased leakage of cell metabolites. Apparently, pyrrolnitrin inhibits fungal growth by inhibiting the respiratory electron transport system.

Antifungal Agents↗
PubMedDate not supplied

Issues in deep space radiation protection.

The exposures in deep space are largely from the Galactic Cosmic Rays (GCR) for which there is as yet little biological experience. Mounting evidence indicates that conventional linear energy transfer (LET) defined protection quantities (quality factors) may not be appropriate for GCR ions. The available biological data indicates that aluminum alloy structures may generate inherently unhealthy internal spacecraft environments in the thickness range for space applications. Methods for optimization of spacecraft shielding and the associated role of materials selection are discussed. One material which may prove to be an important radiation protection material is hydrogenated carbon nanofibers.

Aluminum↗
PubMedDate not supplied

pH-dependent interconvertible forms of mushroom tyrosinase with different kinetic properties.

The lag in cresolase activity and inhibition by excess tyrosine of mushroom tyrosinase which was observed when assayed at pH 6.8 was found to be absent when assayed at pH 5.0. The absence of lag and inhibition by excess tyrosine of tyrosinase at pH 5.0 were brought about only after the enzyme was kept at pH 5.0, at 0-4 degrees C, for 1.5 h. The enzyme kept at pH 5.0 for 1.5-3 h at 0-4 degrees C when brought back to pH 6.8, acquires lag and inhibition by excess tyrosine when its activity was measured at pH 6.8. The pH-dependent changes in the kinetic properties of the mushroom tyrosinase are similar to the pH-dependent changes in the kinetic properties of tyrosinase from B-16 murine melanoma and human skin, and thus appear to be a general property of tyrosinase from diverse sources.

Basidiomycota↗
PubMedDate not supplied

Citrate activates tyrosinase from B-16 murine melanoma and human skin.

Citrate stimulates cresolase activity of tyrosinase from B-16 murine melanoma and human skin. Maximal stimulation by citrate was obtained at 2 mM, and stimulation was decreased at higher concentrations. Citrate stimulates tyrosinase not only from mammalian sources but also from mushroom. The stimulation was not due to reversal of inhibition of enzyme activity by excess tyrosine. On rapid decrease in pH of the enzyme solution from 6.8 to 5.0-5.2, the enzyme is no longer inhibited by excess tyrosine even when its activity was assayed at pH 6.8. Citrate also stimulates this form of enzyme. However, the stimulation is more at acidic pH than at pH 6.8. At higher concentrations of citrate the stimulatory effect decreases at both pH 5.0 and pH 6.8. Inhibition of this enzyme occurs at higher concentrations (22 mM) at pH 6.8. The physiological role of stimulation of cresolase activity of tyrosinase by citrate is yet to be unravelled.

Animals↗