Biomedical subjects
Publications and source records attributed to V Prakash.
Fifty acute SCI patients are reviewed retrospectively for incidence of deep vein thrombosis and pulmonary embolism and the problems encountered in the diagnosis. The possible role of some risk factors in triggering thromboembolism and the consequent implications in anticoagulant therapy are discussed.
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Whole body 99mTc-pyrophosphate scans were obtained and correlated with skeletal radiographs for detection of heterotopic calcification in 122 spinal injury patients. There were 27 patients with recent injury (less than 6 months) and 95 with injury of 6 months to 25 years duration. Ectopic calcification was detected in 8 of the 27 patients (30%) with recent injury and in 32 of the 95 (34%) with injury of over 6 months duration. Ectopic calcification seen on radiographs were also seen on scans in all instances. The scan was a sensitive indicator of the ectopic calcification particularly at its early stage, and detected its presence before observable radiographic changes in 5 patients with injury of 1-3 months duration. In 3 of the 5 patients, the ectopic calcification mimicked deep vein thrombosis in presentation, and the scan was valuable in identifying the nature of the complication.
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The major protein fraction, alpha-globulin, of sesame seed (Sesamum indicum L.) contains subunits which are associated predominantly by hydrophobic interactions. Effects of various salts show the following effectiveness of anions in dissociating the proteins, SO4(2-) less than Cl- less than Br- less than ClO4- less than SCN- less than or equal to I- less than CCl3COO-, the first two members being association-inducing ions. CCl3COONa is found to be the most effective among the series in causing dissociation. The cations Li+, Na+, K+, and Cs+ induce association, the order of effectiveness being Cs+ approximately K+ greater than or equal to Na+ greater than Li+. The low concentration of salts (anions) necessary to induce dissociation does not involve a detectable change in protein conformation. The discrepancy between the effectiveness of the anions in dissociating the protein and the Hofmeister pattern of these ions has been discussed.
The effect of urea and GuHCl on the major protein of sesame seed (Sesamum indicum L.), alpha-globulin, has been investigated by turbidity, sedimentation velocity, viscosity, difference spectra and fluorescence spectral measurements. The protein undergoes dissociation, aggregation and denaturation in the presence of the above denaturants. There is a critical concentration of the denaturant where aggregation is maximum. Both denaturation and aggregation are lower in buffers of high ionic strength. Dissociation and aggregation have been explained by considering two types of subunits present in the protein molecule, one leading to smaller sedimenting component and the other producing the aggregate. The amino acid analysis shows that the aggregated fraction is rich in aliphatic amino acid residues. The endothermic nature of the aggregation process has been considered to arise from hydrophobic interaction of aliphatic side chains of the relevant subunits. The protein exists in a more denatured state in GuHCl than in urea solution.
The association-dissociation and denaturation behaviour of the major protein fraction, alpha-globulin of sesame seed (Sesamum indicum L.), in acid and alkaline solutions in the ranges of pH 4.2-1.5 and pH 7-12 have been studied. The results of gel filtration, fluorescence and viscosity measurements indicate dissociation and denaturation of the protein up to pH approximately 3. The difference spectrum in this region arises from a combination of dissociation, denaturation and charge effect on the chromophore. In still stronger acid solution, reassociation of the dissociated fraction takes place by hydrophobic interaction. In alkaline solution dissociation takes place around pH 8, and above pH 10 dissociation and denaturation proceed simultaneously as has been evidenced by sedimentation, fluorescence, spectral change, optical rotation and viscosity measurements. The phenolic group (pKInt=10.6) in the protein is abnormal and denaturation in alkaline solution is irreversible. Above pH 11.5 further dissociation of the protein takes place. Characteristic pH values of transition from 10.6-10.8 indicate that the transition of the protein involves a single step in alkaline solution.
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The effect of anionic detergent, sodium dodecyl sulphate, on the major protein, alpha-globulin of sesame seed (Sesamum indicum L.) has been investigated by gel filtration, sedimentation velocity, viscosity, optical rotation, difference spectra and fluorescence measurements. The detergent causes dissociation of the protein first and then denaturation. In the detergent concentration range of .175-4.0 X 10(-"3) M four components are observed in the ultracentrifuge. The specific rotation of the protein increases with the detergent concentration above 2.5 x 10 (-3) M detergent suggesting conformational change; above 8 X 10(-"3) M detergent the value of -[alpha] does not change. The reduced viscosity etared however, increases above .25 X 10(-3) M detergent and does not attain a plateau value. The difference spectrum of the protein indicates that both tryptophan and tyrosine groups have been affected by the detergent. The fluorescence intensity decreases and the maxima shifts towards red in the detergent solution resulting in an "isoemissive point" at 355 nm. The double difference spectra in sucrose-detergent protein system show that below 5-0 X 10(-3) M detergent, the difference absorption and fluorescence spectrum result from the binding of the detergent near the chromophoric groups and are not due to conformational change. Binding studies by equilibrium dialysis indicate the presence of 50 binding sites in the protein and binding constant of 3-0 X 10(3).
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N-Acetyl aromatic amino acid esters, tryptophan, adenine and thymine show strong retention in Sephadex LH-20 gel in an aqueous phase. The decreased retention in 6 M urea, the absence of retention in absolute methanol and the increased retention at higher temperatures in the aqueous phase indicate that hydrophobic interaction is responsible for the observed retention of the amino acids and their esters in the gel. Adenine was found to be retained by polar interaction in the gel. The increased retention of the solutes in the presence of different electrolytes suggests that the lyotropic effect is more important than the ionic strength effect. The relevance of the results obtained with amino acids and esters to the conformational aspects of proteins in aqueous solution is discussed.
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