The role of the metal ion in the mechanism of the K+-activated aldehyde dehydrogenase of Saccharomyces cerevisiae

Abstract

The effect of K+ on assays of the enzyme was studied and it appears that the activation occurs slowly by a two-step process. Kinetic measurements suggest that the enzyme-catalysed reaction can proceed slowly (0.4%) in the complete absence of K+. The enzyme exhibits a K+-activated esterase activity, which is further activated by NAD+ or NADH. Stopped-flow studies indicated that the principal effect of K+ on the dehydrogenase reaction is to accelerate a step (possibly acyl-enzyme hydrolysis) associated with a fluorescence and small absorbance transient that occurs after hydride transfer and before NADH dissociation from the terminal E-NADH complex. The variation of activity of the enzyme with pH was studied. An enzyme group with pKa approx. 7.1 apparently promotes enzyme activity when in its alkaline form.