Liver glycogen synthase in rats with a glycogen-storage disorder. The role of glycogen in the regulation of glycogen synthase.

Abstract

1. A strain of rats with a genetically‐determined liver glycogen‐storage disorder (gsd/gsd) caused by a deficiency of liver phosphorylase kinase has a very high concentration of glycogen in the liver with a total glycogen synthase activity higher than in liver of fed normal animals, but only a small amount of the enzyme in the active form. In the livers of both starved and fed normal rats and gsd/gsd rats, there is a positive correlation between glycogen content and total glycogen synthase (r= 0.79) and an inverse correlation between glycogen content and active glycogen synthase (r= 0.86).2. Homogenates of livers from the gsd/gsd rats have lower glycogen‐synthase phosphatase activities than homogenates from fed normal rats which in turn have lower activities than those from starved rats. The addition of glycogen to homogenates of liver from starved rats reduced the glycogen‐synthase phosphatase activity.3. Dilution of homogenates of gsd/gsd rat liver produced an increase in glycogen‐synthase phosphatase activity which could be reversed by adding glycogen.4. The gsd/gsd rats were shown to have liver glycogen‐synthase phosphatase activity comparable to normal rats when the enzyme was measured in dilute homogenates from both groups with the same glycogen concentration.5. It is suggested that inhibition of glycogen‐synthase phosphatase by high glycogen concentrations is responsible for the low levels of activation of glycogen synthase in the gsd/gsd rats and that glycogen itself is probably the major factor controlling glycogen synthesis in gsd/gsd and fed normal rats.