Application of nicotinamide-adenine dinucleotide analogs for clinical enzymology: A spectrophotometric method for clinical analysis of lactate dehydrogenase patterns with the use of a nicotinamide-adenine dinucleotide analog

Abstract

The activities of porcine lactate dehydrogenase(LHD) isoenzymes were analyzed using nicotinamide-adenine dinucleotide(NAD) or its analogs as a cofactor, with varying concentrations of l-lactate from 13 to 530 mM. The greatest differences between H 4-type and M 4-type isoenzymes in reaction rates were observed when their activities were compared in a reaction mixture containing 530 mM lactate and NAD, and also in a system of 13 mM lactate with thionicotinamide-hypoxanthine dinucleotide as a cofactor. The ratio of the LDH activity exerted in the former reaction mixture to that exerted in the latter was termed the N/T value. The N/T values of porcine H 4 and M 4 isoenzymes were 0.49 and 9.33, respectively. The N/T values of other three isoenzymes (H 3M 1, H 2M 2 and H 1M 3) were calculated by assuming that the single subunits H 1 and M 1 contribute one-fourth of the values of 0.49 and 9.33, respectively, and a given isoenzyme which is a combination of four subunits of H and M comprises the sum of their values. The calculated values agreed fairly well with the experimental results. The N/T value method was found to be applicable to human LDH isoenzymes, and sera from various patients were analyzed in comparison with normal sera. The method is particularly suitable for the numerical expression of LDH isoenzyme profiles.