Major differences in isoforms of starch-branching enzyme between developing embryos of round- and wrinkled-seeded peas (Pisum sativum L.)

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Abstract
In order to determine whether round-and wrinkled-seeded peas (Pisum sativum L.) differ in the activity and properties of starch-branching enzyme (1,4-α-D-glucan, 1,4-α-D-glucan-6-glycosyl transferase; EC 2.4.1.18) in their developing embryos, essentially isogenic lines of peas, differing only at the r (rugosus) locus that confers the round (RR, Rr) or wrinkled (rr) phenotype, were studied. Activity of the enzyme rises rapidly from an early stage of development in embryos of round peas, but only at later stages in embryos of wrinkled peas. The purified enzyme from mature embryos of round peas can be resolved into two isoforms that differ in molecular weight and in their ability to branch amylose. The purified enzyme from mature embryos of wrinkled peas is a single protein with the same molecular weight and branching properties as one of the isoforms from embryos of round peas. The difference in activity of starch-branching enzyme between embryos of round and wrinkled peas is likely to be due to the absence from embryos of wrinkled peas of one of the isoforms occurring in embryos of round peas.