PARTIAL-PURIFICATION AND CHARACTERIZATION OF ACID AND NEUTRAL ALPHA-GLUCOSIDASES FROM PRECLIMACTERIC BANANA PULP TISSUES

An acid alpha-glucosidase (AAG) with an optimum pH of 4.5 and two isoforms of neutral alpha-glucosidase (NAG I and II) with an optimum pH of 6.5 were partially purified from preclimacteric banana pulp tissues by monitoring the 4-methylumbelliferyl alpha-D-glucoside (4MUalphaG) hydrolyzing activity. The molecular weights of the AAG and the two NAG were 70,000 and 42,000, respectively, by gel filtration. By kinetic studies, the AAG was found to be a typical maltase that required substrates such as maltose, maltotriose, maltotetraose, and maltopentaose rather than soluble starch. On the other hand, the two NAGs preferred 4MUalphaG to maltose as substrate and their maltase activities were about 50 times lower than that of the AAG. The NAGs, as well as the AAG, did not hydrolyze isomaltose, trehalose, sucrose, or glycogen at all. Sucrose was a competitive inhibitor of the AAG but not NAGs toward 4MUalphaG. Glucose and maltose were also competitive inhibitors of both AAG and NAGs.