Creatine kinase in serum: 2. Interference of adenylate kinase with the assay

Abstract

Interference of adenylate kinase with Oliver's method (1955) for creatine kinase is usually suppressed by including an adenylate kinase inhibitor, AMP. The authors studied the kinetics and compared the inhibition capacities of AMP and diadenosine pentaphosphate. Both are competitive inhibitors, AMP being markedly weaker, with a Ki of about 300 μmol/liter for adenylate kinase from erythrocyte, muscle, and liver. AMP also weakly inhibits creatine kinase. Diadenosine pentaphosphate inhibits erythrocyte and muscle adenylate kinase strongly (Ki about 0.03 μmol/liter), the liver isoenzyme less strongly (Ki about 3 μmol/liter), and has no effect on creatine kinase up to 100 μmol/liter. All three adenylate kinases may be present in a patients's serum, causing sample blanks to be high in a creatine kinase assay that lacks inhibitors. In acute hepatic damage, liver adenylate kinase activity in serum can be grossly increased. Use of sufficient diadenosine pentaphosphate alone for complete inhibition is relatively expensive. Consequently, a combination of both inhibitors is recommended. Diadenosine pentaphosphate, 10 μmol, combined with 5 mmol of AMP per liter inhibits adenylate kinase from erythrocytes and muscle by 97% and from liver by 95%.