IFCC methods for the measurement of catalytic concentration ofenzymes. Part 8. IFCC method for lactatedehydrogenase (L-lactate: NAD+oxidoreductase, EC 1.1.1.27)

[摘要] Human lactate dehydrogenase is a tetramer made up of two typesof subunits, either H (heart) or M (muscle). Combination of thesesubunits gives rise to the five isoenzymes of lactate dehydrogenasewhich are found in mammalian tissues. The relative proportionsof the individual isoenzymes found in serum of patients is relatedto the severity of the lesion in the organ or tissue from which theyoriginate and the half-life of the individual tissue-specific enzymes.Thus, one cannot predict the relative proportions of the differentisoenzymes in any one patient sample.Lactate dehydrogenase catalyses the reversible oxidation of lactateto pyruvate and either reaction can be measured readily. However,in this method, the lactate to pyruvate reaction has been selectedbecause of the following reasons; the time-course of the reaction ismore linear, the reaction results in an increase in absorbance andoptimization of substrates is possible (see appendix A).The principles applied in the selection of the conditions ofmeasurement are those stated in previous publications by the IFCC’sCommittee on Enzymes [1]. Human serum and tissue extracts havebeen used as the sources of enzymes. The final concentration ofsubstrates and the pH have been selected on the basis of experimentsand empirical optimization techniques and have been confirmed bycalculation from rate equations. The catalytic and physicalproperties of the isoenzymes differ, but because of the importance ofthe heart specific isoenzyme (LD1) in the assessment of coronaryheart disease and as a tumour marker, this method has beenoptimized for this isoenzyme. However, the method is also suitable,although less optimally, for the determination of the otherisoenzymes of lactate dehydrogenase which may be present in serum.

[学科分类] 分析化学