KINETIC-PARAMETERS OF 2 RICE ALPHA-AMYLASE ISOZYMES FOR OLIGOSACCHARIDE DEGRADATION

The rice alpha-amylase isozymes Amy1A and Amy3D have distinct kinetic parameters and product profiles, For Amy3D, Michaelis constants (K-m) decrease, and molecular activities (k(cat)) increase with the chain le ngth of the substrates from maltose to maltoheptaose. Although Amy1A h as a lower K-m than Amy3D, the k(cat) of Amy1A was much lower than tha t of Amy3D. Amy1A produces only negligible amounts of glucose, while A my3D produces glucose as a major product. Glucose regulates the expres sion of a number of genes in developing seedlings, so Amy3D may have a unique regulatory role in control of seedling development.