Abstract: | Lactate dehydrogenases at physiological concentrations are inhibited by high concentrations of pyruvate when the enzyme and the pyruvate are incubated in the presence of oxidized nicotinamide-adenine dinucleotide before assay. The inhibition is much more pronounced with the H-type than with the M-type lactate dehydrogenase. These results suggest that substrate inhibition may be operative in vivo. |