Size Distribution of Dispersing Units in Corn Amylose

As the first step to reveal the size distribution of dispersing units in amylose, an amylose sample from corn starch was subjected to gel-filtration chromatography on columns of Sephadex G 200 and Sepharoses 6 B, 4 B and 2 B under protection of the sample from retro-gradation by the use of thiocyanate in the solvent system in the chromatography,

A considerable amount of dispersing units with unexpectedly large size was detected in the amylose sample as a. fraction which was excluded from gels of Sepharoses, though the size distribution was considered to be rather continuous covering the units with smaller size of the regular amylose in the sample. The excluded fraction involved an appreciable amount of aggregates of amylose but no usual amylopectin. Nevertheless, the fraction involved some α-1,6 glucosidic linkages susceptible to isoamylase. The digest of the fraction by the enzyme gave a product which showed size distribution similar to that of the regular size of amylose in the original sample. Both the digested product and the regular amylose had much larger size in molecular weight than the digest of amylopectin by the same enzyme.

The results indicate that the corn amylose sample is a mixture of the units with regular size amylose and those with very large one, the latter having various numbers of branches with the size of regular amylose. Thus, it is considered that the size of dispersing units in the corn amylose sample is characterized as a pattern of such continuous distribution ranging from few hundred thousand up to more than several million in terms of molecular weight.