Evidence for an Essential Carboxyl Group in Glycogen Phosphorylase

Phosphorylase b is rapidly inactivated by 5-diazo-1H-tetrazole or by 1-cyclohexyl-3-(2-morpholinoethyl) carbodiimide metho-p-toluenesulfonate in the presence of glycine ethyl ester. In either case, incorporation of approximately 1 mol of reagent per mole of monomer results in complete inactivation. Consideration of the conditions for inactivation and the known specificity of the carbodiimide reagent suggests that modification of a carboxyl group may be causing the inactivation.