Identification of lactate dehydrogenase isoenzymes by rapid kinetics.

Stopped-flow kinetics indicate that human and chicken heart-type(4) lactate dehydrogenases (LDH) become inhibited as DPNH is oxidized in the presence of high concentrations of pyruvate. This inhibition is much less marked with the human and chicken muscle-type(4) enzymes. The initial rates and the difference in inhibition between the two types of enzyme have made it possible to determine the amount of, as well as the ratio between, the two types of LDH that are present in a given sample by a single kinetic assay. The stopped-flow kinetic method has been used to analyze amounts of LDH isoenzyme in different tissues, as well as in serum.