Misconceptions regarding basic thermodynamics and enzyme kinetics have led to erroneous conclusions regarding the metabolic importance of lactate dehydrogenase isoenzyme expression.Lactate dehydrogenase (LDH) catalyzes the interconversion of pyruvate and lactate involving the coenzyme NAD+ .  First, in line with the general concept of chemical catalysis, enzymes do not influence the thermodynamic equilibrium of a chemical reaction but merely the speed at which equilibrium is obtained.  Second, the thermodynamic equilibrium of the reaction is toward the reduced substrate (i.e., lactate), which is reflected in the concentrations measured in brain tissue, suggesting that the reaction is at near-equilibrium at steady state. 
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