DERIVATIVES OF CINNAMIC ACID INTERACT WITH THE NUCLEOTIDE-BINDING SITE OF MITOCHONDRIAL ALDEHYDE DEHYDROGENASE - EFFECTS ON THE DEHYDROGENASE REACTION AND STIMULATION OF ESTERASE-ACTIVITY BY NUCLEOTIDES

A wide variety of cinnamic acid derivatives are inhibitors of the low K(m) mitochondrial aldehyde dehydrogenase. Two of the most potent inhi bitors are alpha-cyano-3,4-dihydroxythiocinnamamide (K(i) 0.6 muM) and alpha-cyano-3,4,5-trihydroxycinnamonitrile (K(i) 2.6 muM). With propi onaldehyde as substrate the inhibition by these compounds was competit ive with respect to NAD+. Alpha-fluorocinnamate was a much less effect ive inhibitor of the enzyme, with mixed behaviour towards NAD+, but wi th a major competitive component. These cinnamic acid derivatives were ineffective as inhibitors of the aldehyde dehydrogenase-catalysed hyd rolysis of p-nitrophenyl acetate, but inhibited the ability of NAD+ an d NADH to activate this activity. Inhibition of the stimulation of est erase activity was competitive with respect to NAD+ and NADH, and the derived K(i) values were the same as for inhibition of dehydrogenase a ctivity. NAD+, but not acetaldehyde, could elute the low K(m) aldehyde dehydrogenase from alpha-cyanocinnamate-Sepharose, to which the enzym e binds specifically (Poole RC and Halestrap AP, Biochem J 259: 105-11 0, 1989). The cinnamic acid derivatives have little effect on lactate dehydrogenase, glyceraldehyde-3-phosphate dehydrogenase or a high K(m) aldehyde dehydrogenase present in rat liver mitochondria. It is concl uded that some cinnamic acid derivatives are potent inhibitors of the low K(m) aldehyde dehydrogenase, by competing with NAD+/NADH for bindi ng to the enzyme. They are much less effective as inhibitors of other NAD+-dependent dehydrogenases.