Enzymic Conversion of Amylose into Amylopectin

Abstract

POTATO juice was shown by Hanes¹ to contain a phosphorylase (P-enzyme) by the agency of which the long, largely unbranched chains of the amylose component of starch were built up from glucose-1-phosphate. The main component of potato starch is, however, the branched-chain component (amylopectin), and this is not synthesized by P-enzyme acting alone on glucose-l-phosphate. An investigation instituted by Haworth, Peat and Bourne² of the enzyme system of the potato resulted in the isolation of a second enzyme (Q-enzyme) which, in conjunction with P-enzyme, effected the synthesis of amylopectin from glucose-l-phosphate^3,4. The cross-linking enzyme (Q-enzyme) possesses a dual function. In addition to its synthetic activity, it also functions as an amylase in effecting the hydrolytic, as opposed to the phosphorolytic, degradation of amylose⁴. The synthesis and degradation of starch by the agency of P- and Q-enzymes is schematically represented in the paper by Bourne and Peat³.