Studies on the structure of the amylose and amylopectin components of starch

Abstract

The enzymic and physical techniques used in this work have "been discussed in detail. An enzymic assay for the determination of the purity of araylose has "been developed, and the kinetics of the degradation "by 0-amylase of amylose, amylopectin and glycogen examined. The application of low-speed ultracentrifugation to the determination of molecular weight has also "been critically examined.The effect of pretreating starches with various reagents has "been studied in detail. Methanol-pretreatment of the starch granule has been shown to give a completely linear subfraction of amylose on leaching. Pretreatment of starch granules with liquid ammonia has been found to be the most suitable method to ensure satisfactory fractionation.Z-enzyme has been shown to cause a random hydrolytic cleavage of a-1:U bonds in amylose and amylopectin, but to have no effect on glycogen. Barriers to the action of 0-amylase have been introduced artificially by treating hot solutions of amylose with oxygen, and the possibility that the barrier normally present in amylose is an artefact discussed. The action of an acid phosphatase has been shown not to alter the 0-amylolysis limit of amylose, and hence toe possibility that esterified phosphate constituted toe barrier to the action of 0-amylase has been discarded.Subfractionation of amylose has been found to yield evidence for the presence of a slightly branched fraction, toe branching constituting toe barrier to 0-amylolysis. Amylose has been shown to exist in solution as a random coil.An anomalous fraction of amylopectin has "been isolated and shown to he more closely related to normal amylopectin than to glycogen. The significance of this with respect to current theories for the biosynthesis of starch has been discussed.The molecular size and shape of omylopectin from various botanical sources has been determined, and the influence of esterified phosphate on the hydrodynamic behaviour of the molecule discussed.