THE DEGREE OF STARCH PHOSPHORYLATION IS RELATED TO THE CHAIN-LENGTH DISTRIBUTION OF THE NEUTRAL AND THE PHOSPHORYLATED CHAINS OF AMYLOPECTIN

The chain length distribution of the amylopectin neutral and phosphory lated alpha-glucan chains of isoamylase (EC 3,2.1.68)-debranched starc h in dependence of starch phosphorylation has been analyzed using high performance anion-exchange chromatography with pulsed amperometric de tection (HPAEC-PAD). Neutral chains of moderately phosphorylated starc hes showed polymodal distributions with main peaks at dp (degree of po lymerisation) 14-15 and 50, respectively. Highly phosphorylated starch es specifically showed an increasing proportion of chains with mean dp 19. In the extremely highly phosphorylated curcuma (Curcuma spp.) sta rch, this chain population dominated the chain length profile. The sub -population of the corresponding phosphorylated chains from highly pho sphorylated starches showed longer retention times than moderately pho sphorylated starches on HPAEC. Separation of the phosphorylated chains using anion-exchange chromatography at neutral pH demonstrated a part ial separation of chains containing G1c3P residues and G1c6P residues, respectively, as well as a separation of chains containing one or sev eral phosphate groups. Major determinants for the observed elution cha racteristics of phosphorylated chains using HPAEC are suggested to be a combination of chain length (as determined by gel-permeation chromat ography), multiple phosphorylation of the chains (as determined from t heir content of G1c6P and reducing ends) and finally, the presence of the phosphate group on either the C-3 or the C-6 position on the gluco se moieties (as determined by P-31 NMR). The results demonstrate that general rules exist in the relationship between starch phosphorylation and chain length distribution of starches. (C) 1998 Elsevier Science Ltd. All rights reserved.