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Biomedical subjects

V Prakash

Publications and source records attributed to V Prakash.

At least 91 records · Page 5Linked to original sources
PubMed1989

Mechanism of interaction of O-amino-D-serine with sheep liver serine hydroxymethyltransferase.

The mechanism of interaction of O-amino-D-serine (OADS) with sheep liver serine hydroxymethyltransferase (EC 2.1.2.1) (SHMT) was established by measuring changes in the enzyme activity, absorption spectra, circular dichroism (CD) spectra, and stopped-flow spectrophotometry. OADS was a reversible noncompetitive inhibitor (Ki = 1.8 microM) when serine was the varied substrate. The first step in the interaction of OADS with the enzyme was the disruption of enzyme-Schiff base, characterized by the rapid disappearance of absorbance at 425 nm (6.5 X 10(3) M-1 s-1) and CD intensity at 430 nm. Concomitantly, there was a rapid increase in absorbance and CD intensity at 390 nm. The spectral properties of this intermediate enabled its identification as pyridoxal 5'-phosphate (PLP). These changes were followed by a slow unimolecular step (2 X 10(-3) s-1) leading to the formation of PLP-OADS oxime, which was confirmed by its absorbance and fluorescence spectra and retention time on high-performance liquid chromatography. The PLP-OADS oxime was displaced from the enzyme by the addition of PLP as evidenced by the restoration of complete enzyme activity as well as by the spectral properties. The unique feature of the mechanism proposed for the interaction of OADS with sheep liver SHMT was the formation of PLP as an intermediate.

Animals↗
PubMed1989

Mode of interaction of aminooxy compounds with sheep liver serine hydroxymethyltransferase.

The interaction of aminooxy compounds such as aminooxyacetate (AAA), L-canaline, and hydroxylamine with sheep liver serine hydroxymethyltransferase (EC 2.1.2.1) was studied by absorption spectra and stopped-flow spectrophotometry and compared with the unique feature of interaction of O-amino-D-serine (OADS) with the enzyme [Baskaran, N., Prakash, V., Appu Rao, A. G., Radhakrishnan, A. N., Savithri, H. S., & Appaji Rao, N. (1989) Biochemistry (preceding paper in this issue)]. The reaction of AAA (0.5 mM) with the Schiff base of the enzyme resulted in the formation of pyridoxal 5'-phosphate (PLP) and was biphasic with rate constants of 191 and 19 s-1. The formation of the PLP-AAA oxime measured by decrease in absorbance at 388 nm on interaction of AAA with the enzyme had a rate constant of 5.2 M-1 s-1. On the other hand, the reaction of L-canaline with the enzyme was slower as measured by the disruption of enzyme-Schiff base than the reaction of OADS and AAA. In contrast, the formation of PLP as an intermediate could not be detected upon the interaction of hydroxylamine with the enzyme. The reaction of D-cycloserine with the enzyme was much slower (1.6 x 10(2) M-1 s-1) than the aminooxy compounds. These observations indicate that the aminooxy compounds that are structural analogues of serine (OADS, AAA, and canaline) formed PLP as an intermediate prior to the formation of oxime, whereas with hydroxylamine such an intermediate could not be detected.

Acetates↗
PubMed1989

Resistance of alpha-globulin from Sesamum indicum L. to proteases in relationship to its structure.

alpha-Globulin, the high-molecular-weight protein fraction from Sesamum indicum L., was hydrolyzed to low-molecular-weight protein and peptides by pepsin, while its resistance to hydrolysis by group-specific enzymes, trypsin or alpha-chymotrypsin, was very high. The protein showed definite structural changes after proteolysis, especially after peptic hydrolysis, as evidenced from various biophysical data. The sedimentation velocity pattern of alpha-globulin hydrolyzed by trypsin or alpha-chymotrypsin indicated reduction in the percentage of 11S component, while the pepsin-hydrolyzed sample was devoid of any 11S component, indicating the absence of a native protein molecule. The fluorescence emission spectra of the various hydrolyzed alpha-globulin showed a red shift in the fluorescence emission maximum. The red shift was maximum with alpha-globulin hydrolyzed by pepsin and minimum with the trypsin-hydrolyzed sample. The far-ultraviolet-circular dichroic measurements indicated that most of the ordered structure of alpha-globulin was absent after pepsin hydrolysis, while after trypsin and chymotrypsin hydrolysis conformational changes were less.

Alpha-Globulins↗
PubMed1989

Effect of acidic pH on the protein carmin from safflower seed (Carthamus tinctorius).

The effect of a decrease in pH on the structural integrity of carmin has been monitored by a variety of biophysical techniques. The protein undergoes initial dissociation up to pH 3.5-4.0 without any significant denaturation. Below this pH the process of dissociation and denaturation appears to be simultaneous. Further, in the pH range of 2.5-1.6 the protein reassociates to probably a different polymer resulting from possibly, an entropically driven hydrophobic interaction. The process of dissociation appears to be reversible to a large extent. The process of denaturation appears to be governed by the kinetic path that the denatured protein molecule follows either by a sudden decrease in pH or through a gradual decrease in pH. These results are interpreted while keeping in view the oligomeric and globular structure of carmin at neutral pH. The results would help in understanding of structure-function relationship of the protein and its role in hydrogen ion binding in vivo.

Chemical Phenomena↗
PubMed1989

Influence of detergents and pH on the isolation, purification and molecular properties of alpha-galactosidase-C2 from germinating guar (Cyamopsis tetragonolobus).

alpha-Galactosidase was isolated from germinating guar. The extract also contained small amounts of alpha-mannosidase and beta-mannosidase activities. The fractionation of the enzyme extract with ammonium sulphate (75% saturation) resulted in the appearance of all the three enzymes in a floating lipid complex. The inclusion of detergents such as Triton X-100 and sodium deoxycholate in the extraction medium failed to prevent the appearance of these enzymes in the floating lipid complex. However, by using acetone powder of the seedlings, alpha-galactosidase could be sedimented with ammonium sulphate. The presence of detergents in the extraction medium affected the molecular properties of the enzyme. Using a set of carefully selected conditions alpha-galactosidase was purified to apparent homogeneity. Analytical ultracentrifugation and gel filtration studies of the purified enzyme showed association-dissociation phenomenon as a function of pH and temperature. The effect of pH on the association-dissociation indicates the predominance of electrostatic interactions in the association of subunits.

Chemical Phenomena↗
PubMed1989

Post sclerotherapy esophageal ulcers: a prospective analysis of their behaviour.

The reported incidence of post sclerotherapy esophageal ulcers has shown marked variation, possibly due to lack of uniform criteria for their diagnosis. Using fixed criteria (size greater than or equal to 5 mm, duration greater than or equal to 2 weeks), we prospectively studied 82 patients with portal hypertension, who underwent four or more sessions of endoscopic sclerotherapy (EST), for the occurrence and behaviour of these ulcers. Post sclerotherapy ulcers occurred after 43 (9.2%) of 465 EST sessions in 30 (36.6%) of 82 patients. Ulcers were significantly associated with two complications: rebleed during the course of sclerotherapy (33% of ulcers bled compared to 3% from variceal rupture; p less than 0.001) and esophageal stricture formation (66.7% of strictures occurred in patients who had ulcers; p less than 0.05). Ulcers occurred more frequently in patients with poor liver function (61.5% in Child's C grade compared with 31.9% in Child's A or B grades; p less than 0.05) and after injection into larger varices (83.7% in varices grades 3 and 4, 16.3% in lower grades; p less than 0.005). Severe persistent chest pain (p less than 0.001) and pyrexia (p less than 0.01) after sclerotherapy were clinical pointers of ulcerogenesis.

Adult↗
PubMed1988

Association-dissociation and denaturation-renaturation of high-molecular-weight protein: carmin from safflower seed (Carthamus tinctorius L.) in alkaline solution.

The effect of alkaline pH on the association, dissociation, and denaturation of carmin, the high-molecular-weight protein from safflower seed was investigated in the pH range 7-12, using various biophysical techniques. The results indicate that the multimeric protein carmin dissociates at pH 8.0 where denaturation has not set in. The association-dissociation of the protein can be represented schematically as 11S in equilibrium 7S in equilibrium 4S----2S. Above pH 10, the protein undergoes simultaneous dissociation and denaturation. The denaturation process appears to be complete at approximately pH 12.5. The protein undergoes conformational change and covalent modifications and cleavage during the denaturation process. A reversibility study shows that the process of dissociation is reversible to a large extent, whereas denaturation appears to be irreversible. These results are discussed in terms of association-dissociation, denaturation and alkaline-catalyzed covalent modifications and cleavage of seed proteins.

Hydrogen-Ion Concentration↗
PubMed1986

Shape and quaternary structure of alpha-globulin from sesame (Sesamum indicum L.) seed as revealed by small angle x-ray scattering and quasi-elastic light scattering.

The alpha-globulin from sesame seed has a molar mass of 2.7 X 10(5) g mol-1, determined by x-ray scattering, and (2.8 +/- 0.3) 10(5) g mol-1, determined by quasi-elastic light scattering. The radius of gyration RG amounts to (4.1 +/- 0.1) nm and (3.9 +/- 0.2) nm as determined by Guinier approximation and from the distribution function D(x), respectively. The molecule has a Stokes radius Rs of (5.4 +/- 0.15) nm and a maximum dimension L of (11 less than L less than 15) nm. The translational diffusion coefficient D0(20),w and the ratio of fractional coefficients f/fmin amount to (3.95 +/- 0.12) X 10(-7) cm2 s-1 and 1.25, respectively. The quaternary structure of the protein molecule is approximated by a model consisting of six spherical subunits situated at the vertices of an octahedron having the symmetry 32.

Alpha-Globulins↗
PubMed1986

Physicochemical properties of oilseed proteins.

This review attempts to consolidate the information on the physicochemical properties of proteins from groundnut, soybean, sesame seed, mustard seed, rapeseed, sunflower seed, cottonseed, and other oilseeds. It deals with the extraction and characterization of the oilseed proteins and describes the methods for isolation of the various protein fractions and determination of their physicochemical characteristics. Also discussed are the subunit composition of the oligomeric proteins, their hydrodynamic properties, and the effect of denaturants on these proteins. The similarity in the properties of the proteins from various oilseed materials is discussed. The review article aims to indicate the gaps in our knowledge about the physicochemical properties of oilseed proteins and suggests areas for future investigation.

Amino Acids↗
PubMed1985

Vincristine-induced self-association of calf brain tubulin.

The vincristine-induced self-association of tubulin has been examined in a sedimentation velocity study as a function of free drug concentration in PG buffer (0.01 M NaPi and 10(-4) M GTP, pH 7.0) at 20 degrees C. Analysis of the weight-average sedimentation coefficient (S20,w) as a function of protein concentration showed a good fit with the model of an indefinite, isodesmic self-association mechanism. Analysis of the apparent association constants in terms of the Wyman linkage relations showed a good fit to mediation of the self-association by the binding of one ligand molecule. The intrinsic association constant for dimerization of the vincristine-liganded tubulin was found to be 3.8 X 10(5) M-1, and the intrinsic equilibrium constant for the binding of the self-association-linked vincristine molecule had a value of 3.5 X 10(4) M-1, consistent with that measured by fluorescence in our laboratory [Prakash, V., & Timasheff, S. N. (1983) J. Biol. Chem. 258, 1689-1697]. Both reactions are stronger in the presence of vincristine than of vinblastine, reflecting the oxidation of a -CH3 group to -CHO when going from the latter drug to the former one.

Animals↗
PubMed1985

Serum copper in myocardial infarction--diagnostic and prognostic significance.

Serum copper estimations were carried out in 44 cases of acute myocardial infarction, 23 cases of angina and 40 age and sex matched healthy controls. A highly significant degree of rise in serum copper levels was observed in patients with acute myocardial infarction as compared to cases of angina and controls. The levels showed a gradual rise with peak on 7th day followed by a gradual decline returning to normal on 28th day. The pattern was the same both in complicated and uncomplicated cases except that values were still higher on the 28th day in complicated cases of acute myocardial infarction. Mean peak serum copper levels were significantly higher (p less than .001) in complicated cases of acute myocardial infarction as compared to uncomplicated cases. Significant correlation was found between serial serum copper changes and creatinine phosphokinase and lactic dehydrogenase levels. The prognostic and diagnostic significance of serum copper has been discussed.

Adult↗