Kinetic studies on NADPH-linked aldehyde reductase from human liver.

The mechanism of D-glucuronate reduction by human liver NADPH-dependent aldehyde reductase was investigated. At pH 7.4 the Km values for NADPH, NADP+, D-glucuronate and L-gulonate were 2.2 microM, 6 microM, 3.2 mM and 6 mM, respectively. Product inhibition studies in the forward direction (reduction of glucuronate) gave a competitive pattern for the inhibition of NADPH oxidation by NADP+ and non-competitive patterns for the other three inhibitions. In the backward direction all patterns appeared to be competitive. Deuterium isotope effects were dependent on the concentration of D-glucuronate and decreased to unity at infinite concentrations of D-glucuronate. Our findings suggest for aldehyde reductase a kinetic mechanism with sequential ordered binding of NADPH and D-glucuronate and random dissociation of NADP+ and L-gulonate.