Structural perturbation of proteins in low denaturant concentrations.

The presence of very low concentrations of the widely used chemical denaturants, guanidinium chloride and urea, induce changes in the tertiary structure of proteins. We have presented results on such changes in four structurally unrelated proteins to show that such structural perturbations are common irrespective of their origin. Data representative of such structural changes are shown for the monomeric globular proteins such as horseradish peroxidase (HRP) from a plant, human serum albumin (HSA) and prothrombin from ovine blood serum, and for the membrane-associated, worm-like elongated protein, spectrin, from ovine erythrocytes. Structural alterations in these proteins were reflected in quenching studies of tryptophan fluorescence using the widely used quencher acrylamide. Stern-Volmer quenching constants measured in presence of the denaturants, even at concentrations below 100 mM, were higher than those measured in absence of the denaturants. Both steady-state and time-resolved fluorescence emission properties of tryptophan and of the extrinsic probe PRODAN were used for monitoring conformational changes in the proteins in presence of different low concentrations of the denaturants. These results are consistent with earlier studies from our laboratory indicating structural perturbations in proteins at the tertiary level, keeping their native-like secondary structure and their biological activity more or less intact.

Preoperative and postoperative study of left ventricular function, hemodynamics and plasma catecholamine concentrations during dynamic exercise in patients with chronic mitral regurgitation.

We studied 7 patients before and after mitral valve replacement (MVR) for chronic mitral regurgitation (MR) and 5 control subjects by echocardiography and right heart catheterization to assess left ventricular function, hemodynamics and plasma catecholamine concentrations during supine bicycle exercise. Left ventricular (LV) end-systolic dimension decreased and LV systolic function increased significantly during exercise in patients and control subjects. LV systolic function (fractional shortening and mean velocity of circumferential fiber shortening) was significantly lower in patients after MVR than before MVR (p < 0.05). Cardiac index at peak exercise was significantly higher in patients after MVR than before MVR (p < 0.05). Significantly greater augmentation in plasma norepinephrine (NE) levels were observed during exercise in patients both before and after MVR than in control subjects (p < 0.05). No significant differences in mean pulmonary artery pressure (PAP) and pulmonary capillary wedge pressure (PCWP) were observed between the patients before and after MVR. Thus, it is concluded that LV systolic and pump function (CI) during exercise were augmented by a compensatory activation of sympathetic nervous system in patients both before and after MVR for chronic MR.

Chronic diarrhoeal diseases in adults (a preliminary report).

The relationship of chronic diarrhoeal diseases in adults on socio-economic condition, parasitic infestation and degree of anaemia have been investigated. The disease was more prevalent in poor socio-economic group of people. Most of the patients had mixed parasitic infestations. Anaemia was present in all the cases. Difference in the degree of anaemia was not significant amongst the patients having either Ascaris or hookworm infestation.