BETA-AMYLASE FROM TAP ROOTS OF ALFALFA

-beta-Amylase was purified from tap roots of alfalfa (cv Hi-Phy) using techniques to enrich beta-amylase activity, while simultaneously separating it from alpha-amylase activity. Proteins in crude extracts were precipitated with polyethylene glycol and ethanol, followed by ammonium sulphate fractionation, gel filtration and ion exchange chromatography. The purified beta-amylase migrated as a single polypeptide with a M(r) of 57 500 using SDS-PAGE. When electrophorcsed using native polyacrylamide gel electrophesis and blotted into starch-containing gels, several beta-amylase isoforms were evident, beta-Amylase from alfalfa tap roots readily hydrolysed amylopectin, and to a lesser extent, soluble starch, releasing maltose. It also hydrolysed amylose and glycogen; however, activity was lower with these glucans than with amylopectin or soluble starch. No activity was detected when beta-limit dextrin was used as substrate. The purified beta-amylase had a pH optimum of 7.5, which is higher than those from most other sources.