| Abstract: | Investigations into the nature of the effect of the amylose-extender (ae) mutant of maize (Zea mays L.) on amylopectin structure were conducted by studying the fine structure of amylose-extender waxy (ae wx) starch. Approximately 59.6% of the starch from ae wx endosperms was converted to maltose by β-amylase. This starch contained 21% apparent amylose and had a λmax of 580 for the iodine-starch complex. Fractionation of ae wx starch on Sepharose 4B-200 gave an elution profile with a single peak characteristic of amylopectin. From these observations we concluded that ae wx starch consisted of an altered amylopectin, with iodine binding properties such that an apparent amylose content of 21% was measured. The fine structures of ae wx and waxy (wx) starches were determined. Pullulanase-debranched chains of whole starches and β-limit dextrins were fractionated by gel permeation. The amylopectin of ae wx was shown to be a loosely branched amylopectin with an average internal chain length of 52 glucose units compared with a length of 30 glucose units for wx. The ae wx outer chains were longer than those of wx and fewer in number per mg of starch. These characterizations demonstrate that ae wx starch has a unique structure which is similar to the anomalous amylopectin reported in ae starch. |
