Abstract
Two distinct groups of a-amylase isozymes (designated Amylase-I and -III) in suspensioncultured rice (Oryzae sativa L. cv. Sasanishiki) were characterized. These two enzymes differed from the a-amylase found in germinating rice seeds in molecular weight, isoelectricpoint, and Km for soluble starch. The Amylase-III showed a unique property with a low-temperature optimum at 25°C unlike other plant, animal and microbial amylases that generally had optimum at around 35-55°C. The Arrhenius plot for the enzyme also gave an unusual curve, that is, the plot deviated very much from a straight line above 25°C. This suggests the occurrence of a conformational change in the structure of Amylase-III around 25°C in the presence of substrate. By treatment of the Amylase-III with raw starch or maltodextrin (G17) at various temperature (4°C, 26°C and 37°C), the residual amylolytic activity was almost lost.
