The Purification and Properties of the NAD‐Linked Aldehyde Dehydrogenase from Pig Brain

Abstract

The NAD‐linked aldehyde dehydrogenase from pig brain has been purified some 90‐fold over extracts of acetone powders of whole brain. This preparation of enzyme is unstable, and a less pure, more stable preparation has been used to investigate some of the properties of the enzyme. Inhibition of the enzyme by the monoamine oxidase inhibitors 2‐phenylethylhydrazine and 2‐phenyl‐1‐methylethylhydrazine is reported. Ethanol and reserpine have both been found not to inhibit aldehyde dehydrogenase. On the basis of inhibition by o ‐iodosobenzoate and phenylarsenious oxide it is proposed that the enzyme has two juxtaposed sulphydryl groups at or near the active site. Irreversible inhibition by certain conjugated, unsaturated aldehydes is reported. Non‐enzymic reactions of NAD + with indole‐3‐acetaldehyde and phenylacetaldehyde are described. The reaction products are spectrally similar to NADH, but by enzymic criteria are not NADH. It is postulated that the products are the adducts between the aldehydes and the nicotinamide moiety of the coenzyme.