Affinity glycogen synthetase to crosslinked glycogen.

The affinity of yeast glycogen synthetase to glycogen modified by crosslinking has been studied under various experimental conditions. It was found that the higher the degree of crosslinking, the lower the affinity of glycogen synthetase to glycogen. The amount of glycogen synthetase adsorbed from the solution depends on the amount of crosslinked glycogen added and is inversely proportional to the concentration of the soluble glycogen. The stability of the complex formed between yeast glycogen synthetase and the crosslinked glycogen was found to be maximal at neutral pH range. The presence of glucose 6-phosphate, uridine 5′-di-phosphate, and uridine 5′-diphosphate glucose enhanced the stability of the complex.     

Inactivation of skeletal glycogen synthetase by diethylpyrocarbonate

Glycogen synthetase from skeletal muscle is rapidly inactivated by DEPC. In the presence of the substrate UDPG only 50% of the enzyme activity is lost. The concomitant addition of both UDPG and the allosteric activator glucose-6-phosphate almost completely prevents the inactivation by DEPC. Since glucose-6-phosphate alone does not prevent the inactivation by DEPC, it is concluded that it is effective through a potentiation of the effects of UDPG, possibly through a conformational change of the enzyme.     

In vitro activation of leukocyte glycogen synthetase

The activity of leukocyte glycogen synthetase in a freshly prepared homogenate is almost completely in the $\text{b}$ form. Incubation of the homogenate at 30°C caused a time dependent increase in the activity measured in the absence of G-6-P ($\text{b}$ to $\text{a}$ conversion). The K_a for G-6-P decreased from 0.7 to 0.01 mM. Freezing of the homogenate resulted in a complete loss of the capacity for activation. These results demonstrate that glycogen synthetase from leukocytes of normal human subjects can be converted $\text{in vitro}$ to a form, which is almost independent of G-6-P for activity.