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Biomedical subjects

N Kishore

Publications and source records attributed to N Kishore.

At least 19 recordsLinked to original sources
PubMed2005

Structural, optical, physical and electrical properties of V2O5.SrO.B2O3 glasses.

The present work aims to study the structure and variation of optical band gap, density and dc electrical conductivity in vanadium strontium borate glasses. The glass systems xV2O5.(40-x)SrO.60B2O3 and xV2O5.(60-x)B2O3.40SrO with x varying from 0 to 20 mol% were prepared by normal melt quench technique. Structural studies were made by recording IR transmission spectra. The fundamental absorption edge for all the glasses was analyzed in terms of the theory proposed by Davis and Mott. The position of absorption edge and hence the value of the optical band gap was found to depend on the semiconducting glass composition. The absorption in these glasses is believed to be associated with indirect transitions. The origin of Urbach energy is associated with the phonon-assisted indirect transitions. The change in both density and molar volume was discussed in terms of the structural modifications that take place in the glass matrix on addition of V2O5. dc conductivity of the glass systems is also reported. The change of conductivity and activation energy with composition indicates that the conduction process varies from ionic to polaronic one.

Boron Compounds↗
PubMed1998

A thermodynamic investigation of reactions catalyzed by tryptophan synthase.

Microcalorimetry and high-performance liquid chromatography have been used to conduct a thermodynamic investigation of the following reactions catalyzed by the tryptophan synthase alpha 2 beta 2 complex (EC 4.2.1.20) and its subunits: indole(aq) + L-serine(aq) = L-tryptophan(aq) + H2O(1); L-serine(aq) = pyruvate(aq) + ammonia(aq); indole(aq) + D-glyceraldehyde 3-phosphate(aq) = 1-(indol-3-yl)glycerol 3-phosphate(aq); L-serine(aq) + 1-(indol-3-yl)glycerol 3-phosphate(aq) = L-tryptophan(aq) + D-glyceraldehyde 3-phosphate(aq) + H2O(1). The calorimetric measurements led to standard molar enthalpy changes for all four of these reactions. Direct measurements yielded an apparent equilibrium constant for the third reaction; equilibrium constants for the remaining three reactions were obtained by using thermochemical cycle calculations. The results of the calorimetric and equilibrium measurements were analyzed in terms of a chemical equilibrium model that accounted for the multiplicity of the ionic states of the reactants and products. Thermodynamic quantities for chemical reference reactions involving specific ionic forms have been obtained. These quantities permit the calculation of the position of equilibrium of the above four reactions as a function of temperature, pH, and ionic strength. Values of the apparent equilibrium constants and standard transformed Gibbs free energy changes delta r G'(m) degree under approximately physiological conditions are given. Le Châtelier's principle provides an explanation as to why, in the metabolic pathway leading to the synthesis of L-tryptophan, the third reaction proceeds in the direction of formation of indole and D-glyceraldehyde 3-phosphate even though the apparent equilibrium constant greatly favors the formation of 1-(indol-3-yl)glycerol 3-phosphate.

Amino Acids↗
PubMed1998

Prediction of maximal aerobic power in healthy Indian males 21-58 years of age.

An attempt has been made in this paper to predict maximal aerobic power (VO2max) in healthy Indian males by three important physical characteristics (viz. age, height and body weight) using the technique of multivariate regression analysis for a wide age group ranging from 21 to 58 years. It has been observed that these characteristics can contribute significantly to the prediction of maximal aerobic power. Three combinations of predictors of two predictors at a time have also been tried to predict maximal aerobic power. Out of these three combinations, the combination of age and body weight has the maximum multiple correlation (R = 0.536, P < 0.001) for a group of 146 subjects of healthy Indian males. A nomogram has been constructed to predict VO2max from age and body weight in order to make the developed multiple linear regression equation of more practical utility to the biomedical scientists who may not be well acquainted with the statistical computational work.

Adult↗
PubMed1996

Head and chest circumferences as predictors of low birth weight in Indian babies.

This study attempts to select predictors for indirect estimation of low birth weight from three important anthropometric measurements (viz. body length, head and chest circumferences) taken at birth. The data of 422 Indian low birth weight babies have been used to select the best combination of predictors by examining the separate effect of each of the three concomitant variables on birth weight using the technique of multivariate regression analysis. The combination of head and chest circumferences was found to be the best combination of predictors for estimation of birth weight in view of the simplicity and non-invasiveness of measuring these two body circumferences. A nomogram has also been constructed to predict low birth weight from head and chest circumferences. This nomogram will serve as a simple and quick procedure for predicting low birth weight from head and chest circumferences whenever the direct weighing at birth is not feasible.

Anthropometry↗
PubMed1994

Thermodynamic effects of reduction of the active-site disulfide of Escherichia coli thioredoxin explored by differential scanning calorimetry.

Intramolecular disulfide bonds in protein molecules, whether present in the wild-type protein or engineered via site-directed mutagenesis, are capable of significantly increasing the stability. Establishing thermodynamic parameters associated with the redox formation of this linkage is often encumbered by other global structural changes within the protein molecule. The active site of Escherichia coli thioredoxin possesses a disulfide/dithiol in a short loop, oxidation/reduction of which is accompanied by little structural alteration of the protein. Data for the thermal denaturation of the reduced protein are presented, which on comparison to the data obtained for the oxidized form [Ladbury, J.E., Wynn, R., Hellinga, H.W., & Sturtevant, J.M. (1993) Biochemistry 32, 7526-7530] are used to establish thermodynamic parameters for the redox reaction in this molecule. Data for an isosteric double mutation in the active site of thioredoxin (Cys32Ser/Cys35Ser) are also presented. Although the wild-type and mutated proteins show a similar reduction in free energy compared to the oxidized form (-3.0 +/- 0.4 and -3.1 +/- 0.3 kcal mol-1, respectively), the enthalpic and entropic contributions to this destabilization are different for the two proteins.

Binding Sites↗
PubMed1994

Thermodynamics of lectin-carbohydrate interactions. Titration microcalorimetry measurements of the binding of N-linked carbohydrates and ovalbumin to concanavalin A.

The thermodynamics of binding of concanavalin A (Con A) with a series of linear and branched chain oligosaccharides including certain N-linked complex type and oligomannose type carbohydrates and a fraction of quail ovalbumin containing Man7 and Man8 oligomannose chains have been determined using titration microcalorimetry. Methyl3,6-di-O-(alpha-D-mannopyranosyl)-alpha-D-mannopyranoside, a branch chain trisaccharide moiety found in all N-linked carbohydrates which possesses approximately 60-fold higher affinity than methyl alpha-D-mannopyranoside, exhibited a change in enthalpy of binding (delta H) of -14.4 kcal mol-1 as compared to -8.2 kcal mol-1 for the monosaccharide. This demonstrates that Con A possesses an extended binding site for the trimannoside. However, a biantennary complex type carbohydrate with terminal beta (1,2)-GlcNAc residues which binds with 3-fold higher affinity than the trimannoside possesses a delta H of only -10.6 kcal mol-1. A plot of -delta H versus -T delta S for the carbohydrates in the present study showed positive deviations in -T delta S for the complex type carbohydrate, as well as alpha (1,2)-di- and trimannosyl oligosaccharides which are part of the structures of oligomannose type carbohydrates. The relative favorable changes in binding entropies of these compounds are attributed to the presence of multiple internal and terminal residues in each molecule which can independently bind to the monosaccharide binding site of the lectin. The delta H values for the complex type carbohydrate and the alpha (1,2) mannose oligosaccharides were also approximately -2.5 kcal mol-1 greater than that of methyl alpha-D-mannopyranoside, indicating some extended binding site interactions.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1994

Thermodynamics of the hydrolysis of penicillin G and ampicillin.

Apparent equilibrium constants and calorimetric enthalpies of reaction have been measured for the beta-lactamase catalyzed hydrolysis of penicillin G(aq) and ampicillin(aq) to penicillinoic acid(aq) and to ampicillinoic acid(aq), respectively. High-pressure liquid-chromatography and microcalorimetry were used to perform these measurements. The results for the reference reactions at T = 298.15 K and Im = 0 are: Ko = (9.4 +/- 3.1) x 10(-7), delta rGo = (34.4 +/- 1.0)kJ mol-1, delta rHo = -(73.7 +/- 0.4)kJ mol-1, and delta rSo = -(363 +/- 4) J K-1 mol-1 for penicillin G-(aq) + H2O(1) = penicillinoic acid2-(aq) + H+(aq); Ko = (6.0 +/- 3.0) x 10(-6), delta rGo = (29.8 +/- 1.7) kJ mol-1, delta rHo = -(70.0 +/- 7.5) kJ mol-1, and delta rSo = -(335 +/- 26) J K-1 mol-1 for ampicillin-(aq)+ H2O(1) = ampicillinoic acid2-(aq)+H+(aq). Calorimetric enthalpies of reaction for the beta-lactamase catalyzed hydrolysis of cephalosporin C have also been measured but the reaction products have not been identified and the measured enthalpies cannot be assigned to a specific reaction. Acidity constants for ampicillin, penicillin G, ampicillinoic acid, and penicillinoic acid are also reported. A strain energy of 116 kJ mol-1 for the beta-lactam ring is obtained from thermochemical data.

Ampicillin↗
PubMed1990

Height-weight relationship in young healthy Indian males.

Height-weight relationship in young healthy Indian males (19-22 yrs.) has been established. It is concluded that the relationship of the form: log w = 1.18 + 0.35 h fits well to the data on height h (in metres) and weight w (in kilograms) for this group of subjects, the logarithm is taken to the base 10. The results of the present study show that Ehrenberg's equation of the form: log w = 0.8 h + 0.4 cannot be extended beyond the age of 18 years in young healthy Indian males.

Adult↗
PubMed1989

Thermodynamics of some nucleic acid bases and nucleosides in water, and their transfer to aqueous glucose and sucrose solutions at 298.15 K.

The partial molar heat capacities and volumes of some of the constituents of nucleic acids have been determined in water and 1 molal aqueous glucose and sucrose solutions in order to elucidate the nature of interactions occurring between various nucleic acid bases, nucleosides and the sugar (glucose and sucrose) molecules. The results have been explained in terms of the contributions from hydrophobic interactions, hydrophilic interactions and the hydrogen bonding between the solute and solvent molecules. The results have also been compared with those of amino acids and peptides in aqueous glucose and sucrose solutions.

Adenine↗
PubMed1988

The fluid-phase binding of human C4 and its genetic variants, C4A3 and C4B1, to immunoglobulins.

Covalent binding of the fourth complement protein, C4, to immune complexes is an important first step in the complement mediated processing of the complexes. Many of the initial encounters between the proteins of the complement system and antigen and antibody occur in solution, and prior to this report, studies of the interactions between them have focused on complement binding to preformed immune precipitates that most likely are not found in vivo. We have characterized the covalent binding of C4b to immunoglobulin molecules in a fluid-phase system consisting only of antibody in solution and purified C4 and C1s. We demonstrate that human C4b binds to IgG in the fluid phase, that its covalent binding is predominantly to the heavy chain of IgG, and that the covalent linkage is by either amide or acyl ester bonds. In addition, we compare the covalent binding efficiencies of two genetic variants of C4, C4A3 and C4B1, to IgG. C4A3 binds 3-4 times more IgG than C4B1 over a range of C4 concentrations, and C4A3 has a higher binding efficiency than C4B1 for IgM, IgA, IgG2a and F(ab')2 as well as for a protein antigen, BSA. Furthermore, we found that whereas C4A3 is bound to immunoglobulins in the fluid-phase predominantly by amide linkage, C4B1 is bound by either amide or acyl ester bonds. The results presented here suggest that the covalent binding efficiency of C4A3 and C4B1 to IgG is similar to that reported for their covalent binding to small molecules.

Chemical Phenomena↗