Crystalline glycerophosphate dehydrogenase from rabbit muscle.

Enzymatic activity was determined in an optical test, based on the measurement of reduced DPN at 340 rnp in the Beckman spectrophotometer. The reaction was carried out in phosphate or cysteine buffer at pH 7. Synthetic dihydroxyacetone phosphate (5) with reduced DPN or racemic cr-glycerophosphate with DPN was used as substrate to measure the forward and backward reactions, respectively. The concentrations of reactants are given in Tables I and II. The protein concentration was measured optically at 280 mr; the conversion factor for log lo/l readings was obtained from protein determinations by the biuret method of Robinson and Hogden (6).