Hydrolysis of amylopectin by the alpha-amylase of B. subtilis

Abstract

The mixture of oligosaccharides obtained after initial hydrolysis of waxy-maize amylopectin by the alpha-amylase from Bacillus subtilis was fractionated on a Sepharose CL 6B column. The molecular-weight-distribution curves indicated that intermediate products of defined molecular weights were formed as the reaction proceeded towards smaller dextrins. The results can be explained in terms of the cluster model for the fine structure of the amylopectin molecules, assuming that the intermediate products represent one or more unit clusters or cluster residues. Simultaneously with the formation of the intermediate products of molecular weights ⩾30,000, small dextrins were also produced, most probably representing the residues from outer chains in the macromolecule. Thus, alpha-amylase does not hydrolyse amylopectin molecules in a random manner, but, in the initial stages, preferentially attacks the glucosidic bonds between the unit clusters, which in turn are of defined sizes.