p56lyn catalyzes a reversible autophosphorylation reaction and a nucleoside diphosphate kinase reaction

The reversible autophosphorylation of the pp60c-src family tyrosine kinase, p56lyn has been characterized by a simple procedure that involves the examination of the enzyme catalyzed radioisotope exchange between ATP and ADP. The equilibrium constant of the reaction was determined to be 3.31 and corresponded to a standard free energy of hydrolysis of the phosphotyrosine bond in p56lyn of -8.08 kcal/mol. GDP was capable of substituting for ADP as phosphate acceptor so that p56lyn displayed a nucleoside diphosphate kinase activity.