TEMPERATURE-DEPENDENCE OF ACTIVITY AND CONFORMATIONAL-CHANGES IN ALPHA-AMYLASES WITH DIFFERENT THERMOSTABILITY UPON ADSORPTION ON ULTRAFINESILICA PARTICLES

alpha-Amylases from Bacillus subtilis and Bacillus licheniformis, whic h has high thermostability, were adsorbed on ultrafine silica particle s at various temperatures, The activities of adsorbed alpha-amylases w ere measured using corn starch as a substrate. In addition, the circul ar dichroism spectra of adsorbed alpha-amylases were measured, and the alpha-helix contents were calculated to discuss the extent of,conform ational changes quantitatively, The extent of activity reductions upon adsorption of B. subtilis alpha-amylase on the ultrafine silica parti cles was correlated closely with that of conformational changes, and b oth of them were significantly increased by raising temperature from 4 to 40 degrees C. Moreover, they showed stronger temperature dependenc es at lower adsorption amount and pH. On the other hand, the extent of activity reductions and conformational changes upon adsorption of B, licheniformis alpha-amylase on the ultrafine silica particles was much smaller and was not affected by temperature up to 40 degrees C, indic ating the strong influence of stability of enzymes on their molecular states on the solid surfaces, The mechanism of thermal deactivation of alpha-amylases upon adsorption was clearly explained by the direct ob servation of their conformational states on the solid surfaces. It sho uld be noted that the thermal unfolding of adsorbed enzymes takes plac e in a much lower temperature range than that of free ones and is stro ngly affected by the adsorption conditions. (C) 1995 Academic Press, I nc.