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Biomedical subjects

S C Rao

Publications and source records attributed to S C Rao.

26 records · Page 2Linked to original sources
PubMed1989

Binding site conformation dictates the color of the dye stains-all. A study of the binding of this dye to the eye lens proteins crystallins.

The interaction of the cationic carbocyanine dye Stains-all (1-ethyl-2-[3-(1-ethyl-naphthol[1,2-d]thiazolin-2-ylidene)-2- methylpropenyl]naphthol[1,2-d]thiazolium bromide) with the eye lens proteins crystallins has been studied. alpha- and gamma-crystallins do not bind the dye, while beta- and delta-crystallins do, consistent with the fact that the latter two proteins bind the calcium ion. beta-Crystallin resembles parvalbumin in that it induces only the J-band of the bound dye. delta-crystallin, on the other hand, induces only the gamma-band. Analysis of the metachromasia induced in the dye by these and other proteins suggests that Stains-all is responsive to the conformational status of the region to which it binds in a protein. The J-band of the dye is activated when it binds to a globular domain, and the gamma-band is activated when it binds to a helical stretch of the protein.

Animals↗
PubMed1989

Calcium ion binding to delta- and to beta-crystallins. The presence of the "EF-hand" motif in delta-crystallin that aids in calcium ion binding.

Abnormal levels of endogenous calcium ions are known to induce eye lens opacity, and a variety of causative factors has been proposed, including calcium-mediated aggregation and precipitation of the lens proteins crystallins. We have specifically looked in some detail at the interaction of Ca2+ with various crystallins and its consequences. Lenses incubated in solutions containing 10 mM Ca2+ or 5 mM Tb3+ opacified. Fluorescence titration of crystallins with TbCl3 revealed that this ion binds to delta- and beta-crystallins in solution. Equilibrium dialysis showed that four Ca2+ ions bind to one delta-crystallin tetramer with an affinity of 4.3 x 10(3) M-1. Analysis of the amino acid sequence of delta-crystallin reveals the presence of a calmodulin-type "helix-loop-helix" or "EF-hand" calcium ion binding conformational motif in the region comprising residues 300-350. This is a novel feature of the molecule not reported so far. No other crystallins appear to have this motif. beta-Crystallin also binds four Ca2+ ions/aggregate unit of mass 160 kDa, with an affinity of 2.6 x 10(3) M-1, presumably in the midregion of the molecule that is rich in anionic and polar residues. Circular dichroism spectroscopy shows that the binding of calcium ion leads to subtle conformational changes in the molecules, notably in the tertiary structure.

Amino Acid Sequence↗
PubMed1989

Red edge excitation effect in intact eye lens.

Shift in the wavelength of emission upon shift in the excitation wavelength towards the red edge of the absorption band is termed Red Edge Excitation Shift (REES). This effect is observed only in situation where the fluorophore mobility with respect to the surrounding matrix is considerably reduced. We have observed such red edge excitation effect in the intact eye lens. The REES observed for a normal lens is different from that seen in a photodamaged lens and hence appears to be a potential tool to monitor the changes in the state of the lens. Photodamage experiments with tryptophan in polyethylene glycol (PEG) and intact eye lens indicate that the red edge photon can also cause photodamage.

Animals↗
PubMed1988

Is vidian neurectomy worthwhile?

Vasomotor rhinitis is a frustrating experience both for the consultant and for the patient. The purpose of vidian neurectomy is to destroy the secretomotor nerve supply to the nasal mucosa, the main indication being severe intractable non-atopic vasomotor rhinitis. A review of 208 cases which have undergone transnasal vidian neurectomy by diathermy coagulation in the last five years is presented. The operation has proved worthwhile, the patients remaining symptom-free in 92 per cent of cases (longest follow-up 5 years). There have been no complications.

Adolescent↗
PubMed1988

Processed oat hulls as potential dietary fiber sources in rats.

Processed oat hull products were evaluated as potential dietary fiber sources. Three levels, 5, 10 and 15%, of processed oat hulls, bleached oat hulls or oat hulls coated with starch, were added to purified diets and fed to groups of rats for 6 wk. Control diets consisted of 5, 10 or 15% alpha-cellulose or commercial nonpurified diet. None of the oat hull products at the three levels tested had any negative effect on rat growth. Fresh and dry fecal weights increased linearly as the concentration of dietary fiber increased and were highly correlated with fiber intake (r = 0.95). Apparent digestibility of neutral detergent fiber in all diets was low and apparent calcium absorption was not consistently affected by any diet. None of the oat hull test diets lowered plasma or hepatic cholesterol levels, a finding consistent with the failure to detect mixed-linkage beta-glucans in any of the processed oat hull products. Detailed analysis of the processed oat hull fibers also indicated that they were greater than 95% insoluble fiber and high in cellulose and xylans. Light-microscopy histology of kidney, spleen, pancreas, stomach, duodenum, ileum and colon was normal. The extent of hepatocellular destruction produced by the cholesterol (1%) and cholic acid (0.2%) added to the diet to induce hypocholesterolemia was independent of the kind and amount of dietary fiber.

Absorption↗