D-Enzyme: a Disproportionating Enzyme in Potato Juice

Abstract

THE synthesis of amylose is catalysed by the enzyme phosphorylase, which effects a reversible transglucosylation reaction between glucose-1-phosphate and chains of α-1: 4-linked glucose units. Hitherto this has been the only known plant enzyme capable of effecting the synthesis of α-1: 4-glucosidic linkages. We now have to report the discovery of an enzyme in the potato which can effect the synthesis and degradation of (short) amylose-type chains by transglucosylic action. The enzyme was detected in greatest amount in the alcohol-precipitated fraction of potato juice which also contains the greatest amounts of Q-enzyme. The latter enzyme catalyses the conversion of amylose into amylopectin, which involves the simultaneous splitting of α-1 : 4-links and synthesis of α-1: 6-links (an irreversible trans-glycosylation)¹. The new enzyme manifested itself when a Q-enzyme preparation was allowed to act on the linear maltosaccharides produced by the partial acid hydrolysis of amylose². Two effects were noticed. First, iodine-staining material was synthesized from the achroic saccharides and, secondly, paper chromatograms of the digests revealed that the substrates had been disproportionated into products of higher and lower molecular weight, the latter including glucose. For this reason, we have provisionally named the new factor D-enzyme.