Creatine kinase in serum: 3. Further study of adenylate kinase inhibitors

In search of an appropriate inhibitor to suppress the interference of adenylate kinase with the creatine kinase assay, we found that the combination diadenosine pentaphosphate (10 mumol/liter) and AMP (5 mmol/liter) is a better inhibitor than is fluoride (25 mmol/liter). The latter inhibits adenylate kinase uncompetitively and weakly (Ki = 2.5 mmol/liter), and must be incorporated in the starting reagent, and at 30 degrees C it becoms fully effective only after a lag phase of 6 min. In this concentration, fluoride inhibits adenylate kinase from erythrocytes, muscle, liver or platelets by 94, 92, 88, and 87%, respectively, and creatine kinase by 8%. Bromide and chloride also inhibit creatine kinase. Attempts to replace AMP by a specific inhibitor of liver adenylate kinase failed. Homologs of diadenosine pentaphosphate with either fewer or more phosphoryl groups in the polyphosphate bridge inhibited even more weakly than did the pentaphosphate. Platelets can significantly contribute to adenylate kinase activity in serum. The inhibitor combination inhibited adenylate kinase from platelets by 90%.