Purification and Characterization of Soluble and Cell Wall-bound Acid .ALPHA.-Glucosidases of Ripe Yellow Banana Pulp.

Abstract

Purification and characterization of soluble and cell wall bound forms of acid alpha-glucosidases (SAAG and BAAG, respectively; EC 3.2.1.20) from banana are reported. Results showed that banana pulp, irrespective of the degree of ripening, contained both SAAG and BAAG. BAAG was released with a neutral buffer containing 0.2-2M NaCl after extraction of SAAG with a salt-free buffer. From the same bunch of ripe yellow bananas, SAAG and BAAG were purified 732- and 264-fold, respectively, using ConA-Sepharose and Sephadex G-150 gel column chromatographies. The mol. wt. of SAAG and BAAG were estimated to be 70 000 and 90 000 Da, respectively, by gel filtration. These enzymes were typical maltases that required maltose and maltooligosaccharides with up to 7 glucose units as substrates, but not isomaltose, trehalose, sucrose, pullulan, glycogen or soluble starch. The Vmax/Km ratios (apparent hydrolytic efficiencies) of SAAG and BAAG toward maltooligosaccharides comprising 5-7 glucose units were 89-112 and 14-52%, respectively, with the ratio toward maltose being 100%. It is speculated that in ripe yellow banana, where cell wall amyloplastic membrane has not been maintained, BAAG could access starch and starch hydrolysis products, and may share in starch degradation in collaboration with amylases and SAAG.