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Starch Biosynthesis. II. The Statistical Model for Amylopectin and Its Precursor Plant Glycogen
Author(s) -
Erlander Stig R.
Publication year - 1998
Publication title -
starch ‐ stärke
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.62
H-Index - 82
eISSN - 1521-379X
pISSN - 0038-9056
DOI - 10.1002/(sici)1521-379x(199807)50:7<275::aid-star275>3.0.co;2-w
Subject(s) - amylopectin , amylose , branching (polymer chemistry) , glycogen , chemistry , starch , polysaccharide , glycogen branching enzyme , biochemistry , polymer chemistry , chemical engineering , glycogen synthase , organic chemistry , engineering
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.