The Stereospecific Conversion of Stearic Acid to Oleic Acid.

In several enzyme systems that catalyze the desaturation of stearic acid, oleic acid (cis-Ag-octadecenoic acid) is the sole product and the reaction is therefore characterized by positional and geometrical stereospecificity. We now have found that the desaturating system of Corynebacterium diphtheriae has the further property of selectively removing 1 particular hydrogen atom from each pair of hydrogens at carbon atoms 9 and 10 of stearic acid. The enzyme can thus distinguish between the 2 hydrogen atoms attached to a carbon atom of a polymethylene chain. The present report is the first on the stereochemistry of the biological introduction of an isolated double bond into an acyclic compound, and represents a notable example of the stereospecificity of enzymatic reactions at meso carbon atoms (I). Part of this work has been published in preliminary form (2, 3).