Use of 1-methoxy-5-methylphenazinium methyl sulfate (1-methoxyPMS) in the assay of some enzymes of diagnostic importance.

1-Methoxy-5-methylphenazinium methyl sulfate (1-methoxyPMS) is a photochemically stable electron mediator between NAD(P)H and tetrazolium dyes. We have examined the efficiency of 1-methoxyPMS as an electron mediator in the assay of human lactate dehydrogenase (LDH, EC 1.1.1.27) and the activity staining of LDH isozymes after electrophoresis. The turnover number of 1-methoxyPMS as an electron mediator between NADH and nitrotetrazolium blue was 10--12 s-1, which is a value equal to that of PMS. Correlation coefficient between the estimated LDH activities of human sera obtained with 1-methoxyPMS and those obtained with diaphorase was 0.998. 1-MethoxyPMS successfully substituted for the unstable PMS in the activity staining of LDH isozymes of human serum, giving less background staining. We conclude that 1-methoxyPMS will be useful for routine methods of activity assay and activity staining of enzymes of diagnostic importance.