GLYCOGEN PHOSPHORYLASE AND GLYCOGEN SYNTHETASE ACTIVITY IN RED AND WHITE SKELETAL MUSCLE OF THE GUINEA PIG

Histochemically phosphorylase was found to be more active in white than in red muscle fibers but no difference in glycogen synthetase could be detected between the fiber types, however, quantitative determinations showed that total glycogen Synthetase activity was higher in red than in white muscle.

Abstract

Glycogen phosphorylase (α-1,4-glucan:orthophosphate glucosyltransferase) and glycogen synthetase (UDPG:α-1,4-glucan α-4-glucosyltransferase) have been examined in red and white skeletal muscle of the guinea pig. Histochemically phosphorylase was found to be more active in white than in red muscle fibers but no difference in glycogen synthetase could be detected between the fiber types. However, quantitative determinations showed that total glycogen synthetase activity (I + D) was higher in red than in white muscle (1.46 ± 0.14 S.E.M. vs. 0.71 ± 0.09 μmoles/minute per g wet weight at 37°). The converse relationship held for total phosphorylase activity (a + b), which was greater in white than in red muscle (19.24 ± 2.93 vs. 10.43 ± 2.34 μmoles/minute per g wet weight at 30°). The phosphorylase a level of 3.63 ± 0.96 in red muscle at rest was similar to that of 5.44 ± 1.19 in resting white muscle. Stimulation produced a significant conversion of phosphorylase b to a only in white muscle. After 30 seconds stimulation with 1-volt impulses of 20 milliseconds duration at a rate of 20 pulses per second, the phosphorylase a activities of red and white muscle were respectively 3.72 ± 1.88 and 16.66 ± 1.79. After stimulation the glycogen synthetase values in white and red muscle were 1.02 ± 0.07 and 1.72 ± 0.11 respectively.