Starch biosynthesis. Part II: The statistical model for amylopectin and its precursor plant glycogen
1998
Erlander, S.
A modified Meyer model as well as a model containing all possible randomly branched structures (a statistical model) were used for both a precursor glycogen and its amylopectin and were modified by placing short A-chains into the interior part of the structure and thus eliminating some of the longer chains. Debranching of the exterior A-chains of the glycogen model produced amylopectin plus 25 % amylose with the assumption that only those A-chains removed from the glycogen were converted into amylose. A comparison of the debranched amylopectin model with debranched wheat and barley amylopectins showed the polymodal behavior of debranched amylopectins can be duplicated with a model system that has inner A-chains and a Poisson size distribution. Branching of external chains of glycogen without chain extension after synthesis has stopped plus inner A-chains can explain the increase (from glycogen to amylopectin) in the A/B chain ratio, the existance of cluster structures, and the observed decrease in branching (8 % to 4 %) in going from dent, waxy and sweet corn glycogens to their respective amylopectins (or 6.3 % to 2.0 % for glycogen to amylopectin in ae corn). Disperseable (as in waxy) or indispersable high molecular weight aggregates may be due to different amylopectin-protein complexes.
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