Abstract
Uridine diphosphate glucose (UDPG)-glycogen synthetase has been studied using chemical and histochemical methods. Activity was demonstrated in whole egg and in homogenates of whole 3-day old chick embryos, in the heart and skeletal muscle from the 5th day and in the liver from the 7th day of incubation onwards. The activity increases with age until the 16th day at which time a sharp fall was noted in all tissues studied. Enzyme activity was demonstrated also in heart, liver, skeletal muscle and brain of rat embryos from the 14th day onwards. In these tissues the activity increases with age until birth.
The appearance of UDPG-glycogen synthetase in the tissues of the chick embryo coincides with the time at which, according to previously published data, glycogen begins to appear. In the liver of the rat embryo, the enzyme appears before glycogen formation starts. This is contrary to the behavior of phosphorylase which appears later, at least in skeletal muscle. These findings are in agreement with the view that, in vivo, glycogen synthesis occurs via the UDPG, rather than the phosphorylase, pathway.