PubMed Health⌕ Search

Biomedical subjects

R K Mehra

Publications and source records attributed to R K Mehra.

43 records · Page 3Linked to original sources
PubMed1984

Optical and electron paramagnetic resonance spectroscopic studies on purine hydroxylase II from Aspergillus nidulans.

Purine hydroxylase II from Aspergillus nidulans contains a molybdenum cofactor very similar to that found in a number of other molybdenum-containing hydroxylases. (A. nidulans contains two purine hydroxylases, I and II, related to each other by possession of a common cofactor and overlapping substrate specificity.) Addition of reducing substrates effects bleaching of the visible absorption spectrum of the enzyme, the decrease in absorbance at 450 nm being linearly proportional to that at 550 nm. No increase in absorption at longer wavelengths was observed during such titrations. Electron paramagnetic resonance studies of reduced samples of native and modified enzyme species showed the presence of a number of Mo(V) signals (gav = 1.97), exhibiting H hyperfine coupling, comparable to those in the corresponding enzymes from other sources. The enzyme possesses two non-heme-iron-sulfur centers, one (Fe2S2)I with gav less than 2.0 and the other (Fe2S2)II with gav greater than 2.0. The flavin radical signal observed at pH 7.8 had a linewidth of 1.5 mT, indicating it to be the anionic form FAD- . In this respect purine hydroxylase II is unique among all molybdenum-containing hydroxylases studied to date.

Alcohol Oxidoreductases↗
PubMed1984

Measurement of plasma metallothionein-I in the assessment of the zinc status of zinc-deficient and stressed rats.

These studies were designed to investigate the effects of stress and of changes in zinc status on plasma and liver concentrations of metallothionein-I (MT-I) in rats and to assess the value of plasma MT-I assays in the diagnosis of zinc deficiency. No MT-I was detected by radioimmunoassay in the plasma or liver of rats made hypozincaemic by feeding diets with less than 1 or 3 mg Zn/kg. Injection of normal rats with endotoxin or CCl4 also decreased plasma zinc levels, but these treatments greatly increased MT-I concentrations in both liver and plasma. Moreover plasma MT-I levels in zinc-deprived rats given endotoxin were only slightly greater than those in untreated rats of normal zinc status. Neither plasma zinc nor MT-I levels were altered in starved rats despite increased levels of the protein in the liver, although a slight increase in plasma MT-I was found in rats pair-fed with zinc-deficient animals. It appears therefore that reduced plasma levels of both zinc and MT-I are indicative of a zinc deficiency state and that assay of plasma MT should be of value in the diagnosis of zinc deficiency.

Animals↗
PubMed1983

Development of a radioimmunoassay for rat liver metallothionein-I and its application to the analysis of rat plasma and kidneys.

A sensitive radioimmunoassay for rat liver metallothionein-I has been developed using avid and high-titre antibodies obtained from sheep that were immunized with a conjugate of metallothionein and rabbit immunoglobulin G. The assay was specific for metallothionein-I, and did not depend on the particular metal bound to the protein. There was no significant cross-reaction with rat liver metallothionein-II. The use of the assay to measure metallothionein concentrations in rat plasma and kidneys is described.

Animals↗
PubMed1981

Dual control of the gua operon of Escherichia coli K12 by adenine and guanine nucleotides.

The gua operon of Escherichia coli K12 comprises structural genes for the two enzymes, IMP dehydrogenase and GMP synthetase, required for the biosynthesis of GMP from IMP. The specific activities of these enzymes were measured in various purine auxotrophs. GuaA and guaB mutants (guanine-specific) were depressed under conditions of growth limitation by guanine but were repressed by excess guanine. This suggests that formation of the enzymes is normally controlled by a guanine nucleotide. Derepression of the operon in purine-starved pur mutants depended on the type of mutant and on whether adenine or guanine was provided. A purA strain (adenine-specific) and strains with early blocks in purine biosynthesis (purF and purD) did not derepress. PurE or purC strains [5'-phosphoribosyl-5-aminoimidazole (AIR)-accumulating] derepressed only 4-fold. The operon was repressed in purH strains [5'-phosphoribosyl-5-amino-4-imidazolecarboxamide (AICAR)-accumulating] grown with limiting guanine or hypoxanthine, but derepressed by growth with limiting adenine. Two mutants (purA guaA and purA guaB) which can neither synthesize AMP and GMP de novo, nor interconvert them, were isolated. The specific activity of IMP dehydrogenase in one of these strains grown with different concentrations of guanine and adenine revealed that adenine induces tha gua operon whereas guanine represses it. Intracellular purine nucleotide pools wee measured in a purH mutant repressed (guanine-grown) and derepressed (adenine-grown) for IMP dehydrogenase. The guanylate pool was similar under the two growth conditions; however the adenylate pool of the adenine-grown bacteria was two to three times greater than that of the guanine-grown cells. A dual mechanism for regulating expression of the gua operon, involving induction by AMP and repression by GMP, is proposed.

Adenine↗
PubMed1980

Clearance of orally administered 115mCd from rat tissues.

Peak 115Cd levels in the liver, kidneys, spleen and duodenum of the rat, following a single oral dose, fell exponentially. Half-clearance time for 115mCd is highest in the kidney (30 days) followed by the liver (6.8 days), the spleen (5.5 days) and the duodenum (3.5 days).

Administration, Oral↗
PubMed1980

203Hg binding in the liver and kidney of the frog, Rana tigrina.

Following a single i.p. dose of the radioisotope, 203Hg was found to accumulate in both the high and low molecular weight (MW) fractions of the kidney and liver of the frog. The course of 203Hg appearance in the 2 fractions varied in the liver; 203Hg was exclusively associated with the higher MW fractions at 2 days whereas the radiotracer appeared in both low and high MW fractions at 4 and 7 days after administration. In the kidneys, however, 203Hg was associated with high and low MW fractions at all the intervals studied. Low MW 203Hg binding fraction appeared to be a metallothionein-like substance.

Animals↗