NONENZYMATIC ISOMERIZATION OF 9-CIS-RETINOIC ACID-CATALYZED BY SULFHYDRYL COMPOUNDS

Certain thiol-containing compounds catalyze, in a chemical reaction, t he isomerization of g-cis-retinoic acid to a mixture of all-trans-reti noic acid, 9-cis-retinoic acid, 13-cis-retinoic acid, and 9,13-dicis-r etinoic acid. In the presence of such catalysts, all-trans-retinoic ac id gives rise to the same mixture. Reactions approaching equilibrium c ontain more all-trans-retinoic acid than either of the other isomers. Small molecules effective as catalysts are mercaptoethanol, L-cysteine methyl ester, glutathione, and N-acetyl-L-cysteine. Apoferritin (a th iol-containing protein), native microsomes, and, to a lesser extent, b oiled microsomes catalyze the reaction. In intact cells, these interco nversions also occur in a process inhibited by a sulfhydryl-specific r eagent. The thiol-catalyzed isomerization of 9-cis-retinoic acid may b e relevant in the biological activity of this compound.