MECHANISM OF THERMAL AGGREGATION OF RABBIT MUSCLE GLYCERALDEHYDE-3-PHOSPHATE DEHYDROGENASE. BIOCHEMISTRY.

Thermal denaturation and aggregation of rabbit muscle glyceraldehyde-3-phosphate dehydrogenase (GAPDH) have been studied using differential scanning calorimetry (DSC), dynamic light scattering (DLS), and analytical ultracentrifugation. The maximum of the protein thermal transition (T(m)) increased with increasing the protein concentration, suggesting that the denaturation process involves the stage of reversible dissociation of the enzyme tetramer into the oligomeric forms of lesser size. The dissociation of the enzyme tetramer was shown by sedimentation velocity at 45 degrees C. The DLS data support the mechanism of protein aggregation that involves a stage of the formation of the start aggregates followed by their sticking together. The hydrodynamic radius of the start aggregates remained constant in the temperature interval from 37 to 55 degrees C and was independent of the protein concentration (R(h,0) approximately 21 nm; 10 mM sodium phosphate, pH 7.5). A strict correlation between thermal aggregation of GAPDH registered by the increase in the light scattering intensity and protein denaturation characterized by DSC has been proved

EFFECT OF ALPHA-CRYSTALLIN ON THERMAL DENATURATION AND AGGREGATION OF RABBIT MUSCLE GLYCERALDEHYDE-3-PHOSPHATE DEHYDROGENASE.

The study of thermal denaturation of rabbit muscle glyceraldehyde-3-phosphate dehydrogenase (GAPDH) in the presence of alpha-crystallin by differential scanning calorimetry (DSC) showed that the position of the maximum on the DSC profile (T(max)) was shifted toward lower temperatures with increasing alpha-crystallin concentration. The diminishing GAPDH stability in the presence of alpha-crystallin has been explained assuming that heating of GAPDH induces dissociation of the tetrameric form of the enzyme into dimers interacting with alpha-crystallin. The dissociation of the enzyme tetramer was shown by sedimentation velocity at 45 degrees C. Suppression of thermal aggregation of GAPDH by alpha-crystallin was studied by dynamic light scattering under the conditions wherein temperature was elevated at a constant rate. The construction of the light scattering intensity versus the hydrodynamic radius (R(h)) plots enabled estimating the hydrodynamic radius of the start aggregates (R(h,0)). When aggregation of GAPDH was studied in the presence of alpha-crystallin, the start aggregates of lesser size were observed

JHK \u27-band IOTA interferometry of the circumstellar environment of R CrB

We report the first long-baseline interferometry of the circumstellar dust environment of R CrB. The observations were carried out with the Infrared Optical Telescope Array (IOTA), using our new JHK' beam combiner which enables us to record fringes in the J, H, and K' bands simultaneously. The circumstellar dust envelope of R CrB is resolved at a baseline of 21 m along a position angle of similar to170degrees, and the visibilities in the J, H, and K' bands are 0.97 +/- 0.06, 0.78 +/- 0.06, and 0.61 +/- 0.03, respectively. These observed visibilities, together with the K'-band visibility obtained by speckle interferometry with baselines of up to 6 m, and the spectral energy distribution are compared with predictions from spherical dust shell models which consist of the central star and an optically thin dust shell. The comparison reveals that the observed J- and H-band visibilities are in agreement with those predicted by these models, and the inner radius and inner boundary temperature of the dust shell were derived to be 60-80 R-* and 950-1050 K, respectively. However, the predicted K'-band visibilities are found to be similar to10% smaller than the one obtained with IOTA. Given the simplifications adopted in our models and the complex nature of the object, this can nevertheless be regarded as rough agreement. As a hypothesis to explain this small discrepancy, we propose that there might be a group of newly formed dust clouds, which may appear as a third visibility component