FINE-STRUCTURE OF WHEAT AMYLOPECTIN - THE MODE OF A-CHAIN TO B-CHAIN BINDING

The fine structure of wheat amylopectin was analyzed by means of a new enzymic method, as well as by conventional methods. Its general properties were found to be similar to those of rice amylopectin with intermediate iodine affinity, but the chain-length distribution was clearly distinguishable from that of rice amylopectins. The B chain, as defined by Peat and co-workers [J. Chem. Soc. (1956) 3025], was classified into Ba and Bb chains on the basis of whether A chains were bound (Ba) or not bound (Bb), and the number of A chains bound to a Ba chain was determined from the ratio of non-reducing to reducing residues of the stepwise degradation products of the amylopectin with β-amylase, isoamylase, and β-amylase. A Ba chain was found to carry 2.1 A chains on average, but the longer Ba chains bound increased numbers of A chains (up to four). The A: B and the Ba: Bb chain ratios were found to be 1.26:1 and 1.5:1, respectively, indicating that ∼40% of the B chains carried no A chains. © 1990.