Degradation of various starch granules by glucoamylases of Rhizopus amagasakiens,Rhizopus niveus and Endomyces.

Abstract

The action of four preparations of glucoamylase [α-1, 4-glucan glucohydrolase, EC 3. 2. 1. 3], crude glucoamylases of Rhizopus amagasakiens and Endomyces and crystalline glucoamylases of Rhizopus niveus and Endomyces, on starch granules of less susceptible [potato, anaylose-extender (ae) mutant of maize and heat-moisture treated potato] and more susceptible [sugary-2 (su2) and sugary-2 opaque-2 (su2 o2) mutants of maize] types to the action of a-amylase than normal maize was studied to characterize the action of these enzymes on native starch granules. The extent of hydrolysis (percent degradation) was followed by measuring the amount of glucose liberated. Patterns of degradation were observed by scanning electron microscopy (SEM). Each preparation showed qualitatively similar time courses of degradation specific for each respective type of starch granules although each preparation contained different amounts of a-amylase. Relative rate of digestion by glucoamylases of the six types of starch granules showed that su2 and su2 o2 cmutants of maize were most rapid, followed by normal maize, heat-moisture treated potato, ac maize, and potato in decreasing order respectively. Four preparations of glucoamylase showed, in general, similar patterns of attack on the normal maize starch granules. Namely, small pits appeared on the surfaces of the granules, pits increased in number and size and holes penetrated into the inner portions of the granules toward the center of the granules. The points of attack were uniformly distributed on the surfaces of the granules.