Starch Biosynthesis. I. The Size Distributions of Amylose and Amylopectin and Their Relationships to the Biosynthesis of Starch

Abstract

Equations for the size distributions of both linear and branched polymers were applied to debranched amylopectin, linear amylose, and branched amylose polymers. The experimental size distribution of linear amylose corresponds to the broad size distribution of an A–B condensation polymer, whereas that of debranched amylopectin linear chains corresponds to the much narrower Poisson size distribution. These dramatic differences illustrate that different types of enzymes synthesize the linear chains of amylose as compared to those of amylopectin. These results support the previously proposed mechanism. The polymodal behavior of debranched amylopectin is due to the existance of individual Poisson-type polymers created by tier structures in a statistically formed precursor glycogen. Equations were developed which enable the calculation of the percentages of these individual Poisson polymers. When applied to the differences between shx and Bomi barley amylopectins, it is concluded that both studies agree that two different short, inner tier, A-chains exist, where the longer chain is located in the more external third tier in the amylopectins. In amylose, three different polymers exist: A linear amylose A–B type condensation polymer, a branched amylose which behaves as a statistical A–R–B2 type polymer, and an intermediate, non-statistically branched amylose polymer.