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Biomedical subjects

V K Shah

Publications and source records attributed to V K Shah.

At least 55 records · Page 3Linked to original sources
PubMed1989

Purification and characterization of the nifN and nifE gene products from Azotobacter vinelandii mutant UW45.

The nifN and -E gene products are involved in the synthesis of the iron-molybdenum cofactor of dinitrogenase, the enzyme responsible for the reduction of dinitrogen to ammonia. By using the in vitro iron-molybdenum cofactor biosynthesis assay, we have followed the purification of these gene products 450-fold to greater than 95% purity. An overall recovery of 20% was obtained with the purified protein having a specific activity of 6900 units/mg of protein. The protein (hereafter referred to as NIFNE) was found to contain equimolar amounts of the nifN and -E gene products and have a native molecular mass of 200 +/- 10 kDa, which indicates an alpha 2 beta 2 structure. NIFNE was oxygen labile with a half-life of 1 min in air. A UV-visible spectrum of the dye-oxidized protein showed an absorption maximum at 425 nm that could be bleached by reduction of NIFNE with sodium dithionite, suggesting the presence of an Fe center in NIFNE.

Azotobacter↗
PubMed1989

Prognostic significance of predischarge 2D-echocardiography after first transmural myocardial infarction.

Predischarge two dimensional echocardiography (2D Echo) was performed in 45 survivors of first transmural myocardial infarction to assess its value in predicting major cardiac complications (MCC) during convalescence. Wall motion score was derived for each patient by analysing endocardial motion in 11 left ventricular segments. In 18 months follow up 11 of 14 patients (78%) who had major cardiac complications had wall motion score of at least 5. Wall motion score of less than 5 was present in 29 of the 31 (94%) of patients in asymptomatic group. Non-invasively obtained wall motion score helps in risk stratification of survivors of AMI. Wall motion score at predischarge 2D Echo or more identifies high risk cases from a relatively asymptomatic group (Killip Class I & II).

Adult↗
PubMed1988

Dinitrogenase with altered substrate specificity results from the use of homocitrate analogues for in vitro synthesis of the iron-molybdenum cofactor.

The in vitro synthesis of the iron-molybdenum cofactor (FeMo-co) of nitrogenase requires homocitrate (2-hydroxy-1,2,4-butanetricarboxylic acid). Homocitrate is apparently synthesized by the nifV gene product. In the absence of homocitrate, no FeMo-co is formed in vitro, as determined from coupled C2H2 reduction assays and the lack of 99Mo label incorporation into apodinitrogenase. Several organic acids were tested for their ability to replace homocitrate in the FeMo-co synthesis system. With appropriate homocitrate analogues, aberrant forms of FeMo-co are synthesized that exhibit altered substrate specificity and inhibitor susceptibility. Homoisocitrate (1-hydroxy-1,2,4-butanetricarboxylic acid) and 2-oxoglutarate facilitated the incorporation of 99Mo into apodinitrogenase in the FeMo-co synthesis system, yielding a dinitrogenase that effectively catalyzed the reduction of protons but not C2H2 or N2. Citrate also promoted the incorporation of 99Mo into apodinitrogenase, and the resulting holodinitrogenase reduced protons and C2H2 effectively but not N2. In addition, proton reduction from this enzyme was inhibited by CO. The properties of the homodinitrogenase formed in the presence of citrate were reminiscent of those of the Klebsiella pneumoniae NifV- dinitrogenase. We also observed low rates of HD formation from NifV- dinitrogenase compared to those from the wild-type enzyme. No HD formation was observed with the dinitrogenase activated in vitro in the presence of citrate. We propose that in vivo NifV- mutants utilize citrate for FeMo-co synthesis.

Enzyme Activation↗
PubMed1988

Homocitrate cures the NifV- phenotype in Klebsiella pneumoniae.

Dinitrogenase was isolated from a culture of a Klebsiella pneumoniae NifV- strain derepressed for nitrogenase in the presence of homocitrate. The enzyme isolated from this culture was identical to the wild-type dinitrogenase. These data provide in vivo evidence that the absence of homocitrate is responsible for the NifV- phenotype.

Dinitrogenase Reductase↗
PubMed1988

Biosynthesis of the iron-molybdenum cofactor of nitrogenase.

The iron-molybdenum cofactor (FeMo-co) of nitrogenase is a Mo-Fe-S cluster that has been proposed as the site of substrate reduction for the nitrogenase enzyme complex. Biosynthesis of FeMo-co in Klebsiella pneumoniae requires at least six nif (nitrogen fixation) gene products. One of the nif genes, nifV, apparently encodes a homocitrate synthase. The synthesis and accumulation of homocitrate [(R)-2-hydroxy-1,2,4-butanetricarboxylic acid] in K.pneumoniae is correlated to the presence of a functional nifV gene. K.pneumoniae strains with mutations in nifV synthesize and accumulate an aberrant form of FeMo-co. Nitrogenase from NifV- mutants is capable of reducing some of the substrates of nitrogenase effectively (e.g. acetylene), but reduces N2 poorly. With the aid of an in vitro FeMo-co synthesis system, it recently has been established that homocitrate is an endogenous component of FeMo-co. Substitution of homocitrate with other carboxylic acids results in the formation of aberrant forms of FeMo-co with altered substrate reduction capability.

Chemical Phenomena↗
PubMed1987

Double-chambered right ventricle with pulmonary valve endocarditis.

A rare case of isolated pulmonary valve endocarditis associated with a double-chambered right ventricle in a nonaddict, was diagnosed on two-dimensional echocardiography and cardiac catheterization and angiography. The patient was successfully operated and the above findings confirmed on the operation table.

Cardiac Catheterization↗
PubMed1987

Iron-molybdenum cofactor synthesis in Azotobacter vinelandii Nif- mutants.

Nif- mutants of Azotobacter vinelandii defective in dinitrogenase activity synthesized iron-molybdenum cofactor (FeMo-co) and accumulated it in two protein-bound forms: inactive dinitrogenase and a possible intermediate involved in the FeMo-co biosynthetic pathway. FeMo-co from both these proteins could activate apo-dinitrogenase from FeMo-co-deficient mutants.

Azotobacter↗
PubMed1986

In vitro synthesis of the iron-molybdenum cofactor of nitrogenase.

Molybdate- and ATP-dependent in vitro synthesis of the iron-molybdenum cofactor (FeMo-co) of nitrogenase requires the protein products of at least the nifB, nifN, and nifE genes. Extracts of FeMo-co-negative mutants of Klebsiella pneumoniae and Azotobacter vinelandii with lesions in different genes can be complemented for FeMo-co synthesis. Both K. pneumoniae and A. vinelandii dinitrogenase (component I) deficient in FeMo-co can be activated by FeMo-co synthesized in vitro. Properties of the partially purified dinitrogenase activated by FeMo-co synthesized in vitro were comparable to those of dinitrogenase from the wild-type organism; e.g., ratios of acetylene- to nitrogen-reduction activities, as well as those of acetylene reduction activities to EPR spectrum peak height at g = 3.65, were very similar. A. vinelandii mutants UW45 and CA30 have mutations in a gene functionally equivalent to nifB of K. pneumoniae.

Acetylene↗
PubMed1986

nifV-dependent, low-molecular-weight factor required for in vitro synthesis of iron-molybdenum cofactor of nitrogenase.

The molybdate- and ATP-dependent in vitro synthesis of the iron-molybdenum cofactor of nitrogenase requires a low-molecular-weight factor. The factor is present in extracts of nitrogen fixation-derepressed cultures of Klebsiella pneumoniae and Azotobacter vinelandii, but not in extracts of repressed cultures of these bacteria. Analysis of K. pneumoniae Nif mutants has indicated that the nifV gene product is the only nif protein (besides nifA) necessary for the synthesis and accumulation of the factor. The factor is stable to oxygen, temperatures below 120 degrees C, and extremely acidic and basic conditions. The activity of the factor was completely destroyed by dry ashing or digestion with sulfuric acid. The factor has been partially purified by filtration through an Amicon PM-10 DIAFLO membrane and chromatography on DEAE-cellulose, hydroxylapatite, silica gel, and Sephadex G-25.

Azotobacter↗
PubMed1985

Inhibition of iron-molybdenum cofactor binding to component I of nitrogenase.

Tetrathiomolybdate inhibits iron-molybdenum cofactor (FeMo cofactor) binding to component I of nitrogenase. Molybdenum-iron cluster (a subcomponent of FeMo cofactor) and tetrathiomolybdate inhibited FeMo cofactor activation of inactive nitrogenase component I in extracts of Azotobacter vinelandii and Klebsiella pneumoniae mutant strains defective in the biosynthesis of FeMo cofactor. Addition of tetrathiotungstate, the tungsten analog of tetrathiomolybdate, to the mutant extracts had no significant inhibitory effect on subsequent activation by FeMo cofactor.

Azotobacter↗