The purification and some properties of the Mg2(+)-activated cytosolic aldehyde dehydrogenase of Saccharomyces cerevisiae

A purification procedure has been developed for the cytosolic aldehyde dehydrogenase of Saccharomyces cerevisiae that yields homogeneous enzyme. The enzyme seems to be a tetramer of identical 58 kDa subunits. The enzyme reaction is strongly stimulated by Mg2+ at low NADP(+) concentrations but there is no absolute requirement for bivalent cations. The kinetics of the reaction have been studied in the presence and absence of MgCl2. NADP(+) binding studies of the quenching of protein fluorescence in the presence and absence of MgCl2, show that the effect of Mg2+ is to increase the affinity of the enzyme for NADP(+) by approx. 100-fold. NADP(+) binding causes a slow conformational change in the enzyme and converts the enzyme from the inactive or low-activity form in which It Is Isolated into the fully active form. This conformational change seems to explain the marked lag-phases seen in enzyme assays. The enzyme is strongly inhibited by disulfiram and pyridoxal 5-phosphate.