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

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Abstract
Glycogen phosphorylase ([alpha]-1,4-glucan:orthophosphate glucosyltrans-ferase) and glycogen synthetase (UDPG:[alpha]-1,4-glucan [alpha]-4-glucosyltrans-ferase) 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[plus or minus]0.14 S.E.M. vs. 0.71[plus or minus]0.09 [mu]moles/minute per g wet weight at 37[degree]). The converse relationship held for total phosphorylase activity (a + b), which was greater in white than in red muscle (19.24 [plus or minus] 2.93 vs. 10.43[plus or minus]2.34 umoles/minute per g wet weight at 30[degree]). The phosphorylase a level of 3.63[plus or minus] 0.96 in red muscle at rest was similar to that of 5.44[plus or minus]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 [plus or minus] 1.88 and 16.66[plus or minus]1.79. After stimulation the glycogen synthetase values in white and red muscle were 1.02[plus or minus]0.07 and 1.72[plus or minus]0.11 respectively.