Positional specificity of gamma-ketol formation from linoleic acid hydroperoxides by a corn germ enzyme.

We have shown unequivocally that the positional specificity of gamma-ketol formation by a corn germ enzyme was different from that observed previously by others with an alfalfa seedling enzyme. When the pure positional isomers of linoleic acid hydroperoxide served as substrates, the corn germ enzyme formed one of two gamma-ketols: 12-oxo-9-hydroxy-trans-10-octadeconoic acid from 13-hydroperoxys-10-octadecenoic acid from 13-hydroperoxy-cis-9,trans-11-octadecadienoic acid (99+% pure) and 10-oxo-13-hydroxy-trans-11-octadecenoic acid from 9-hydroperoxy-trans-10,cis-12-octadecadienoic acid (96% pure). Also isolated from these reactions was one of two alpha-ketols commonly found as a result of catalysis by linoleic acid hydroperoxide isomerase: 12-oxo-13-hydroxy-cis-9-octadecenoic acid from the 13-hydroperoxide and 10-oxo-9-hydroxy-cis-12-octadecenoic acid from the 9-hydroperoxide. Evidence is offered that gamma-ketol formation is catalyzed by linoleic acid hydroperoxide isomerase, the same enzyme responsible for alpha-ketol production.