Hypothesis on the Mode of Conversion of Glucose into α-Glucose-1-phosphate

Abstract

SOME 10 years ago much evidence had accumulated that phosphorylase does not synthesize glycogen from α-glucose-1-phosphate in vivo. The confirmation of this belief came with the discovery of glycogen synthetase, and its synthesis of glycogen from uridine diphosphate glucose (UDPG)¹. There is now a parallel situation in another area of glycogen metabolism, namely, repeated evidence from tracer experiments that the conversion of glucose into glycogen in liver and muscle does not proceed by way of glucose-6-phosphate. Several reports, originating with Beloff-Chain et al.² and most recently by Threlfall³, combine to indicate that there is a pathway from glucose to α-glucose-1-phosphate—and thence to UDPG and glycogen—that does not have glucose-6-phosphate formation as an intermediate step. In other words, hexokinase, glucokinase, glucose-6-phosphatase acting in its synthetic role, all forming glucose-6-phosphate, together with phosphoglucomutase, converting the 6-phosphate into α-glucose-1-phosphate, may well have no direct role in the conversion of glucose into glycogen.