THE DE NOVO SYNTHESIS OF POLYSACCHARIDE BY PHOSPHORYLASE

Abstract

Highly purified phosphorylase is capable of forming an amylose chain from glucose-1-phosphate in the absence of any primer. The chain does not have a phosphate group at its reducing end. The initial de novo act occurs very slowly and is characterized by an apparently absolute lag period during which no Pi is liberated and no exchange occurs with Pi 32. There follows a more rapid reaction of chain elongation leading to the formation of a product which may become more than 2000 glucose units long. In the presence of highly purified amylo-1,4[long dash]1,6-transglycosidase the rate of polysaccharide formation is enormously increased, and the product of de novo synthesis is glycogen with an end group of 7.5 to 6.3 % and a molecular weight ranging from 2 to 25 million in different experiments. Phosphorylase and the "branching enzyme" together constitute a catalytic system for the de novo synthesis of glycogen, a process which could be of special importance during embryonal development.