On the nature of categories of chains in amylopectin and their connection to the super helix model

Amylopectin of waxy maize and amylose-free potato starch (PAPS) were analysed for their compositions of categories of unit chains. The ratio of A:B-chains was best obtained by debranching of limit dextrins of the amylopectins. Although, an exact ratio was difficult to obtain without adjustments, the discrepancies were small and the ratio was not dependent on the original length of the chains. From the knowledge of the external chain length and the chain distribution of the phi,beta-limit dextrins, the original distributions of A- and B-chains were traced and the chains were grouped into characteristic categories. Clustered chains were represented by a degree of polymerisation (DP) from 9 to 34. A-chains overlapped with 'fingerprint' B-fp-chains (DP 15-20) and constituted probably building blocks inside clusters. The shortest A-chains (A(fp)) at DP 6-8 and all long chains (DPgreater than or equal to35, including long A-chains present in PAPS) were amorphous. In a proposed two-directional backbone model, the clusters are connected to a backbone that extends in a (almost) perpendicular direction and is formed by the amorphous chains. The model makes it possible to construct a super-helical structure from a single amylopectin macromolecule. (C) 2004 Elsevier Ltd. All rights reserved.