RapidAssayfor Glycogen-CycleEnzymesin SmallSamplesof Muscle

A rapid assay is described for the glycogen-cycle enzymes glycogen syn-thetase and a-glucan phosphorylase (UDP glucose:glycogen a-4-glucosyl-transferase, EC 2.4.1.11 and a-1,4.glucan:orthophosphate glucosyltrans-ferase, EC 2.4.1.1) in muscle tissue. UDP gIucose-’C and G-1-P-’C are used as substrates for reaction with muscle homogenates, and the rate of incor-poration of labeled glucose into primer glycogen is measured. Muscle sam-ples weighing 25 to 75 mg are suitable for assay. We found activities in rat gastrocnemius muscle of 0.37 ± 0.02 moI of glucose per minute per gram of tissue for synthetase I, 2.84 ± 0.29 moI per minute per gram of tissue for synthetase D, and 34.5 ± 2.8,moI per minute per gram of tissue for phos-phorylase b. Corresponding values for human muscle tissue for phos-phorylase a and b were 12.6and 10.6moI per minute per gram of tissue, and synthetase activity of 0.011and 0.399Mm0I per minute per gram of tissue. Additional Keyph rases a-glucan phosphorylase #{149} giycogen synthetase human and rat muscle tissue #{149} glycogen synthesis #{149} normal activity value