The kinetics of the reversible inhibition of heart lactate dehydrogenase through the formation of the enzyme-oxidized nicotinamide-adenine dinucleotide-pyruvate compounds.

The inhibition of lactate dehydrogenase at high pyruvate concentration was studied in three ways. First, a rapid decrease in the rate of the enzyme reaction was observed; secondly, the rate of formation of a pyruvate-NAD(+) compound was followed by the change in E(325); thirdly, the rate of quenching of the protein fluorescence was measured. The data obtained at pH6.0 at different temperatures and ionic strengths as functions of pyruvate, NAD(+) and enzyme concentrations show that the extent of inhibition can be correlated with the reversible formation of a compound between pyruvate and enzyme-bound NAD(+). It is suggested that the detailed kinetic analysis of the formation of this abortive ternary compound will give pertinent information about properties of the enzyme-NAD(+) compound involved in the normal catalytic process.