[Turbidimetric method of determination of glycogen synthase activity in rabbit skeletal muscles]

A turbidimetric procedure is described, which involves the monitoring of changes in glycogen turbidity at wavelengths above 300 nm and continuous recording of rabbit skeletal muscle synthase activity. The recalculation coefficients were found to be equal to 1.69 +/- 0.08 mM UDP per unit of optical density at 360 nm and to 2.03 +/- 0.01 mM UDP per unit of optical density at 400 nm. The procedure allows a kinetic analysis of the enzyme within a broad range of concentrations and under various conditions. The glycogen synthase activity did not depend on the buffer capacity when 10-100 mM Tris-HCL buffer, pN 7.8, was used. The rate of the enzymatic reaction was correlated with the enzyme concentration within the range of 5 to 50 micrograms/ml. The curve for glycogen synthase saturation with UDPG is described by the Michaelis-Menten equation, when either 0.04-0.08 mM glucose-6-phosphate for for the D-form were used in mixtures containing 5 mM MgCl2 for the D-form were used in mixtures containing 5 mM MgCl2 and 10 mM Na2SO4. The turbidimetric and spectrophotometric procedures yielded similar results.