Thermal denaturation and aggregation of beta(L)-crystallin from bovine lens have been studied using differential scanning calorimetry (DSC) and dynamic light scattering (DLS). According to the DLS data, the distribution of the beta(L)-crystallin aggregates by their hydrodynamic radius (R(h)) remains monomodal to the point of precipitating aggregates (sodium phosphate, pH 6.8; 100 mM NaCl; 60 degrees C). The size of the start aggregates (R(h,0)) and duration of the latent stage (t(0)) leading to the formation of the start aggregates have been determined from the light scattering intensity versus the hydrodynamic radius plots and the dependences of R(h) on time. The R(h,0) value remains constant at variation of the beta(L)-crystallin concentration, whereas the t(0) value increases with diminishing beta(L)-crystallin concentration. The suppression of beta(L)-crystallin aggregation by alpha-crystallin is connected with the decrease in the R(h,0) value and increase in the t(0) value. In the presence of alpha-crystallin the aggregate population is split into two components. The first component is represented by stable aggregates whose size remains constant in time. The aggregates of the other kind grow until they reach the size characteristic of aggregates prone to precipitation. The DSC data show that alpha-crystallin has no appreciable influence on thermal denaturation of beta(L)-crystallin.

Mechanism of thermal aggregation of protein substrates (bovine lens βL-crystallin; yeast alcohol dehydrogenase; rabbit skeletal muscles glycogen phosphorylase b and glyceraldehydes 3-phosphate dehydrogenase; coat protein of tobacco mosaic virus) has been studied by dynamic light scattering. The stage of denaturation of the proteins under study was characterized using differential scanning calorimetry. It has been established that the aggregation process involves a latent stage, its duration (t0) being determined by the point in time at which the initial increase in the light scattering intensity is observed. The initial parts of the dependences of the light scattering intensity on the hydrodynamic