Effects of univalent cations on the properties of yeast NAD+ acetaldehyde dehydrogenase

Acetaldehyde dehydrogenase (aldehyde:NAD(P)+ oxidoreductase, EC 1.2.1.5) from yeast is activated by K+ and Rb+. Sodium and Li+ antagonize the activation, apparently by competitive inhibition with K+. The stimulation of activity by mercaptoethanol and the activation by K+ are not additive in a reaction mixture containing both. Potassium and Rb+ in the order just mentioned protect acetaldehyde dehydrogenase from inactivation by heat, whereas Na+ and Li+ are less effective as protectants. After prolonged dialysis against Tris buffer, and consequent loss of 90–95% of activity, the enzyme can be reactivated to a considerable extent by univalent cations. The best reactivating cation is K+, followed by Rb+ then by Na+ and Li+ and finally by Tris+. The level of K+ required to half-saturate the enzyme is independent of substrate size.