The equilibrium constants of the glutamate dehydrogenase systems.

1. Equilibrium constants for the oxidation of glutamate by NAD(+) and NADP(+), catalysed by glutamate dehydrogenase, have been measured in phosphate buffers of different ionic strengths and at several temperatures. 2. The equilibrium constants for both systems vary markedly with ionic strength. Thermodynamic values for the two systems obtained by extrapolation to zero ionic strength differ significantly from one another. The standard free-energy change for NADP(+) reduction has been calculated from that for NAD(+) reduction. 3. The heat of reaction has been estimated and is the same with both coenzymes. 4. The thermodynamic data are discussed in relation to earlier data.