α-glucosidase from grape berries: Partial purification and characterization.

α-Glucosidase (α-D-glucoside glucohydrolase EC 3.2.1.20) was purified approximately 30-fold from grape berries (Vitis vinifera var. Riesling). Besides maltose the enzyme preparation hydrolyzes to a lesser extent maltotriose, isomaltose, and starch. It has a pH optimum of 5.1 and a molecular weight of about 100,000. Tris, glycerol, several mono-and disaccharides were tested as inhibitors. The kinetic behavior of ribose, fructose, cellobiose, sucrose, turanose, methylglucopyranoside, Tris, and glycerol was fully investigated. The inhibition studies suggest a Ping-Pong mechanism, with the second substrate concentration being constant, that can be treated as a Uni Bi system. The purified enzyme is stable when stored frozen at-20° C. The grape-berry α-glucosidase may exist as multiple forms (pI 7.2 and 8.2 respectively), and it does not require ions for its activity.