According to the cluster modeP3, amylopectin, the branched component of starch, comprises chains of (l-+4)-linked ~-~-glucopyranosyl residues inter-connects by ( 146) linkages in close groups. It has been shown by gel-permeation chromatography that debranching of amylopectins characteristically givesell short and long chains with average chain lengths (~1.) of 1 l-25 and 40-60 residues, respectively. In several amyIopectins"-'3, the short chains may be divided into two poorly separated groups with c.l. ll-13 and 18-19. The former group probably represents A-chains and the latter group short B-chains (Bl-chains) 14-A-chains do not carry other chains, , whereas B-chains carry A-or B-chains". Hizukuri14 reported a polymodal distribution of the unit chains in many amylo~tins in which groups of long B-chains exist. These so-called B3-and B4-chains have c-1. w 70 and -I 10, respectively, and were suggested to extend into three or more clusters, whereas the major group of long chains (B2chains) extends into two clusters. Small propo~ions of long chains have been reported by other workers'6*'7
When waxy-maize amylop~tin was debranched with isoamylase, gel-ideation chromatography of the products on Sephadex G-50 (Fig. 1) gave two major peaks. The column was calibrated by the method of Mercier and Whelan'* in which the average d.p. in each fraction was dete~ined as the ratio between the total carbohydrate and the content of reducing-end residues. Determination of the latter values by the Nelson reagent for fractions of higher d.p. requires large amounts of the debranched sampie18. However, even when the concentration of the sample was increased from 5 to 10 mg/mL and the volume from 0.5 to 2 mL, it was difficult to determine reproducibly d.p. values of > 30.
The standard curve (Fig. 2) shows a linear relation between log d.p. and K,, 0.2 and 0.8. The calibration at higher d.p. could be estimated only approximately. Based on this calibration, the profiles of the unit chains (Fig. 1) were used to calculate the c.1, of the amylopectin [as .Z_4i/Z(A~d.p.i), in which Aj is the absorbance and d.p., is the d.p. of fraction 9. Similar profiles of the unit chains and values of c.1. were obtained with two concentrations of the sample applied (Table I). However, the values of c-1. were lower than those determined from the concentration of reducing-end groups in the debranched sample prior to gel-pe~eation chromatography and those based on the