PubMed Health⌕ Search

Biomedical subjects

V K Shah

Publications and source records attributed to V K Shah.

At least 19 recordsLinked to original sources
PubMed1992

Plausible structure of the iron-molybdenum cofactor of nitrogenase.

A plausible structure of the iron-molybdenum cofactor of nitrogenase [reduced ferredoxin:dinitrogen oxidoreductase (ATP-hydrolyzing), EC 1.18.6.1] is presented based on altered substrate reduction properties of dinitrogenase containing homocitrate analogs within the cofactor. Alterations on each carbon of the four-carbon homocitrate backbone were correlated with altered substrate reduction properties of dinitrogenase containing these analogs. Altered substrate reduction properties are the basis for a model in which homocitrate is oriented about two cubane metal clusters.

Formates↗
PubMed1991

Uses and limitations of transthoracic echocardiography in the assessment of atrial septal defect in the adult.

Two-dimensional and color Doppler echocardiography accurately detected the presence of an atrial septal defect (ASD) in 47 of 50 adults (mean age 40 years) confirmed by surgery or cardiac catheterization, or both. It correctly categorized all patients with ostium secundum and ostium primum ASD but misdiagnosed 3 of 5 patients with surgically proven sinus venosus ASD. The shunt flow volume across the ASD was calculated with the standard Doppler equation, and assuming the ASD to be circular correlated with shunt flow volume obtained by cardiac catheterization (r = 0.74). The maximum width of the color flow signals moving across the ASD was taken as its diameter. Mean flow velocity was determined either by placing a pulsed Doppler sample volume parallel to the flow across the ASD as visualized by color Doppler or by color M-mode examination, which allowed determination of flow velocities using a previously validated method that incorporates a computer analysis of pixel color intensity. The pulmonary to systemic blood flow ratio obtained by color-guided conventional Doppler interrogation of the left and right ventricular outflow tracts correlated poorly with cardiac catheterization results (r = 0.38). In patients with associated tricuspid regurgitation, the peak systolic pulmonary artery pressure obtained by color Doppler-guided continuous-wave Doppler correlated well with that obtained at cardiac catheterization (r = 0.89). The maximum color Doppler jet width of the flow across the ASD poorly correlated with ASD size estimated at surgery (r = 0.50).

Adolescent↗
PubMed1991

Effects of homocitrate, homocitrate lactone, and fluorohomocitrate on nitrogenase in NifV- mutants of Azotobacter vinelandii.

Azotobacter vinelandii DJ71, which contains a mutation in the nifV gene, was derepressed for nitrogenase in the presence of homocitrate. When dinitrogenase was isolated from this culture, it was found to be identical to the wild-type dinitrogenase. However, when the same NifV- strain was derepressed in the presence of erythrofluorohomocitrate, a homocitrate analog which produces a nitrogenase with wild-type properties in vitro, the isolated dinitrogenase was characteristic of the NifV- enzyme. These data show that homocitrate, but not fluorohomocitrate, is utilized by NifV- mutant cells. Fluorohomocitrate does not inhibit the uptake of homocitrate because the wild-type phenotype resulted when both compounds were added to the medium during nitrogenase derepression. Homocitrate lactone failed to cure the NifV- phenotype.

Azotobacter↗
PubMed1991

Computer modeling and functional evaluation of Venturi flow generators for use in ventilators.

A Venturi has been traditionally used for liquid and gas flow measurements based on Bernoulli and Venturi principles. Application of Venturi as a flow generator in a mechanical ventilator was limited to being a secondary source of flow or configured to compress flexible bags. The main reason for this level of utilization is the considerable flow deterioration of flow output under respiratory system load. A method was hence sought to probe into the possibility of using a Venturi device as the main flow generator with onload flow compensation. The Venturi was mathematically modeled to incorporate the three possible control variables which are controls of jet diameter, entrainment port size and the working pressure of the gas to be entrained. A set of experimental data were then quantitatively compared and evaluated with the results of computer simulation of the TUTSIM model of the system under equivalent conditions. The nature of the results can open up a range of different automatic control schemes and their practical implementation.

Computer Simulation↗
PubMed1990

Citrate substitutes for homocitrate in nitrogenase of a nifV mutant of Klebsiella pneumoniae.

An organic acid extracted from purified dinitrogenase isolated from a nifV mutant of Klebsiella pneumoniae has been identified as citric acid. H2 evolution by the citrate-containing dinitrogenase is partially inhibited by CO, and by some substrates for nitrogenase. The response of maximum velocities to changes in pH for both the wild-type and the NifV- dinitrogenase was compared. No substantial differences between the enzymes were observed, but there are minor differences. Both enzymes are stable in the pH range 4.8-10, but the enzyme activities dropped dramatically below pH 6.2.

Citrates↗
PubMed1990

Apodinitrogenase: purification, association with a 20-kilodalton protein, and activation by the iron-molybdenum cofactor in the absence of dinitrogenase reductase.

The Azotobacter vinelandii mutant strain UW45 contains a mutation in the nifB gene and produces an inactive dinitrogenase protein that can be activated by the addition of purified iron-molybdenum cofactor (FeMoco). This FeMoco-deficient dinitrogenase (Apo I) has now been purified 96-fold to greater than 95% purity and is FeMoco-activatable to 2200 nmol of C2H2 reduced/(min.mg of protein). The Apo I complex was found to contain two molecules of a 20-kDa protein, in addition to the alpha 2 beta 2 tetramer found for isolated holodinitrogenase (Holo I). The Apo I complex contained 15 +/- 2 mol of Fe per mole, but no Mo. While the presence of dinitrogenase reductase caused a 2-fold stimulation in the activation of the purified Apo I complex by FeMoco, this enhancement resulted from the stabilization of Apo I by dinitrogenase reductase to the denaturing effects of N-methylformamide. When the activation was performed in the absence of N-methylformamide, there was no enhancement by dinitrogenase reductase alone or by dinitrogenase reductase-Mg-ATP complex. The Apo I complex is more sensitive to O2 than Holo I, with a half-life in air of 6 min; however, the addition of dithiothreitol to Apo I during the exposure to air (or after exposure) resulted in a half-life very similar to that seen for Holo I. This suggests that sulfhydryl(s) is (are) important for the FeMoco-activation reaction.

Apoenzymes↗
PubMed1990

Diastereomer-dependent substrate reduction properties of a dinitrogenase containing 1-fluorohomocitrate in the iron-molybdenum cofactor.

In vitro synthesis of the iron-molybdenum cofactor (FeMo-co) of dinitrogenase using homocitrate and its analogs allows the formation of modified forms of FeMo-co that show altered substrate specificities (N2, acetylene, cyanide, or proton reduction) of nitrogenase [reduced ferredoxin:dinitrogen oxidoreductase (ATP-hydrolyzing), EC 1.18.6.1]. The (1R,2S)-threo- and (1S,2S)-erythro-fluorinated diastereomers of homocitrate have been incorporated in vitro into dinitrogenase in place of homocitrate. Dinitrogenase activated with FeMo-co synthesized using threo-fluorohomocitrate reduces protons, cyanide, and acetylene but cannot reduce N2. In addition, proton reduction is inhibited by carbon monoxide (CO), a characteristic of dinitrogenase from NifV- mutants. Dinitrogenase activated with FeMo-co synthesized using erythro-fluorohomocitrate reduces protons, cyanide, acetylene, and N2. In this case proton reduction is not inhibited by CO, a characteristic of the wild-type enzyme. Cyanide reduction properties of dinitrogenase activated with FeMo-co containing either fluorohomocitrate diastereomer are similar, and CO strongly inhibits cyanide reduction. Dinitrogenases activated with FeMo-co containing homocitrate analogs with a hydroxyl group on the C-1 position are much less susceptible to CO inhibition of cyanide reduction. However, proton and cyanide reduction by dinitrogenase containing FeMo-co activated with (1R,2S) threo-isocitrate is only one-third that of dinitrogenase activated with the racemic mixture of -isocitrate and shows strong CO inhibition of substrate reduction. These results suggest that CO inhibition of proton and cyanide reduction occurs when the hydroxyl group on the C-1 position of analogs is "trans" to the C-2 carboxyl group (i.e., in the threo conformation). When racemic mixtures of these analogs are used in the system, it seems that the erythro form is preferentially incorporated into dinitrogenase. Finally, carbonyl sulfide inhibition of substrate reduction by dinitrogenase is dependent on the homocitrate analog incorporated into FeMo-co.

Carbon Monoxide↗
PubMed1990

Synthesis of the iron-molybdenum cofactor of nitrogenase is inhibited by a low-molecular-weight metabolite of Klebsiella pneumoniae.

The in vitro synthesis of the iron-molybdenum cofactor nitrogenase was inhibited by a low-molecular-weight factor. This inhibitory factor was present in the membrane extracts of wild-type and nif mutant strains of Klebsiella pneumoniae that were grown under conditions that either repressed or derepressed nitrogenase expression. In vitro, the inhibition was specific for the NifB protein. Addition of this factor to K. pneumoniae cells at various times during nif derepression decreased nitrogenase activity, presumably through inhibition of iron-molybdenum cofactor synthesis. The inhibitor was purified by solvent extraction and chromatography on DEAE-cellulose, silica gel, and aluminum oxide columns.

Bacterial Proteins↗
PubMed1990

Pleomorphic intimal sarcoma of pulmonary artery. A case report.

A rare case of pleomorphic intimal sarcoma of pulmonary trunk is reported. The patient presented with symptoms of right ventricular out flow tract (RVOT) obstruction. Metastatic deposits were seen in lungs, diaphragm and thyroid. Bronchial mucosal involvement was also seen. The tumour showed multicentric origin and on electron microscopic examination in a particular cell line was seen.

Adult↗
PubMed1990

Design of an optimal ventilator.

When a patient is incapable of adequate ventilation by natural processes, mechanical assistance must be provided. Ventilation assures sufficient Oxygen delivery to the organs and tissues of the body and excessive amounts of Carbon Dioxide are not permitted to accumulate. Ventilators are employed continuously or intermittently to improve the ventilation of the lungs. The present work involves design of a ventilator that virtually eliminates any work done by the patients in their breathing process. Presently available ventilators approach this level of performance but they have a few reported shortcomings. These limitations include insufficiency of inspiratory airflow and rigidity of operating cycles. The new ventilator is built around an optimal controller and its performance is based on computational capability of microprocessors. Real time measurements of volume, flow rates and pressure are managed and processed by these devices for optimal determination of controlled parameters of the ensuing respiratory cycle. These measured parameters are used for estimating the lung characteristics such as lung compliance and airway resistance. An independent microprocessor system incorporating data acquisition and processing features with scope for a number of additional capabilities such as graphic output, database and communications functions can prove very useful in health care institutions.

Biomechanical Phenomena↗
PubMed1989

Substrate reduction properties of dinitrogenase activated in vitro are dependent upon the presence of homocitrate or its analogues during iron-molybdenum cofactor synthesis.

(R)-2-Hydroxy-1,2,4-butanetricarboxylic acid [(R)-homocitrate] has been has been recently reported to be an integral constituent of the otherwise thought to be inorganic iron-molybdenum cofactor of dinitrogenase [Hoover, T.R., Imperial, J., Ludden, P.W., & Shah, V.K. (1989) Biochemistry 28,2768-2771]. Different organic acids can substitute for homocitrate in an in vitro system for iron-molybdenum cofactor synthesis and incorporation into dinitrogenase [Hoover, T.R., Imperial, J., Ludden, P.W., & Shah, V. K. (1988) Biochemistry 27, 3647-3652]. Dinitrogenase activated with homocitrate-FeMo-co was able to reduce dinitrogen, acetylene, and protons efficiently. Homoisocitrate and isocitrate dinitrogenases did not reduce dinitrogen or acetylene, but showed very high proton reduction activities. Citrate and citramalate dinitrogenases had very low dinitrogen reduction activities and intermediate acetylene and proton reduction activities. CO inhibited proton reduction in both these cases but not in the case of dinitrogenases activated with other homocitrate analogues. By use of these and other commercially available homocitrate analogues in the in vitro system, the structural features of the homocitrate molecule absolutely required for the synthesis of a catalytically competent iron-molybdenum cofactor were determined to be the hydroxyl group, the 1- and 2-carboxyl groups, and the R configuration of the chiral center. The stringency of the structural requirements was dependent on the nitrogenase substrate used for the assay, with dinitrogen having the most stringent requirements followed by acetylene and protons.

Bacteria↗
PubMed1989

Homocitrate is a component of the iron-molybdenum cofactor of nitrogenase.

When apodinitrogenase (lacking FeMo-co) was activated with FeMo-co synthesized in vitro in the presence of 3H-labeled homocitrate, label was incorporated into dinitrogenase. The physical association of the label with FeMo-co was demonstrated by reisolation and purification of the cofactor from dinitrogenase. The presence of homocitrate in FeMo-co was established by NMR analysis of the organic acid extracted from dinitrogenase. Quantitation of homocitrate in dinitrogenase showed it to be present at a 1:1 ratio with molybdenum.

Chromatography, DEAE-Cellulose↗
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↗