Kinetic studies of the reduction of succinic semialdehyde by rat-brain aldehyde reductase.

Initial rate studies have been used to investigate the kinetic mechanism followed by the purified high-Km (AR1) form of rat brain aldehyde reductase at pH 7.0. The effects of varying the aldehyde and NADPH concentrations, together with the inhibition given by the products of the reaction, are consistent with the reduction of succinic semialdehyde and p-nitrobenzaldehyde following an ordered reaction mechanism involving the formation of an intermediate ternary complex and in which NADPH is the first substrate to bind to the enzyme. Both these aldehyde substrates inhibit the enzyme at higher concentrations. This inhibition, which is uncompetitive with respect to NADPH, suggests that many previous studies on the specificity of this enzyme, that have been based on the activity determined at a single arbitrary concentration of each substrate, may have given erroneous results.