The kinetics of the reversible inhibition of heart lactate dehydrogenase through the formation of the enzyme–oxidized nicotinamide–adenine dinucleotide–pyruvate compound

[摘要]

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 E₃₂₅; 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.