Enzyme kinetics and its relevance to enzyme assay.

The reversible oxidation of lactate by lactate dehydrogenase (EC 1-1 1-27), pH7-4 pyruvate + NADH + H+ 't lactate + NAD+, pH 9 2 may be regarded as a typical enzyme reaction which can proceed in either direction according to whether pyruvate or lactate is provided as substrate. When the reaction is started by the addition of either substrate in the presence of the appropriate coenzyme, pH, temperature, etc, it proceeds quite rapidly at first. However, as substrate or coenzyme is consumed and the products accumulate, the rate gradually slows until an equilibrium is reached at which the forward and reverse reactions proceed at the same rate (Fig. 1).