Deuterium isotope effects on initial rates of the liver alcohol dehydrogenase reaction

Initial steady-state velocities using highly purified deuterated substrates and coenzymes as well as an isoenzymatically homogeneous enzyme preparation were measured for liver alcohol dehydrogenase at 25 deg in 20 mm phosphate (pH 7.0) or 20 mm pyrophosphate (pH 8.8). Significant isotope effects of v/sub 0,H//v/sub 0,D/ were observed. In the reduction of acetaldehyde by A- NADD the isotope effects were found to decrease with increasing acetaldehyde concentration, a result consistent with an ordered Theorell-- Chance mechanism for the reduction of acetaldehyde only at saturating substrate concentrations. No kinetically significant interactions were observed between the enzyme and the untransferred hydrogen of NADH. (auth)