Substitution reactions of linoleic acid hydroperoxide isomerase

Abstract

Linoleic acid hydroperoxide isomerase was extracted from corn germ and partially purified by differential centrifugation. This enzyme catalyzed the isomerization of linoleic acid hydroperoxide.(see article) Isomerase also catalyzed the substitution of various reagents at the carbon bearing the hydroperoxide group. These fatty acid products had the following functional groupings: (see article) where X is either oleoyloxy, ethylthio, or methoxy resulting from the presence of oleic acid, ethanethiol, or methanol, respectively. A crude wheat germ extract containing both lipoxygenase and isomerase enzymes reacted with linoleic acid to yield alpha-ketols, gamma-ketols, and a substitution product, the linoleoyloxy ester of alpha-ketol. Characterization of these products from wheat germ enzymes showed that the substitution reaction was not unique to corn germ. Because anions of the reagents tested are typical nucleophiles, the substitution reactions may proceed by a nucleophilic mechanism as mediated by the isomerase enzyme.

Positional specificity of γ‐ketol formation from linoleic acid hydroperoxides by a corn germ enzyme

“…In addition to the usual products, a-and "y-ketols, substitution compounds resulted. One of these was the oleoyl ester of the c~-ketol, which was a reaction product described by Christianson and Gardner (7). In our study, another substitution compound was identified as the oleoyl ester of 3'ketol.…”

“…Substitution Products. Those products from substitution reactions with either oleic acid or methanol were isolated by silicic acid column chromatography by the methods of Christianson and Gardner (7). The substitution products described here were minor products compared to those described previously (7).…”

“…The enzyme reactions that occurred in the presence of either methanol or oleic acid were described by Christianson and Gardner (7). Chromatography a-and 7-Ketols.…”

“…Those products from substitution reactions with either oleic acid or methanol were isolated by silicic acid column chromatography by the methods of Christianson and Gardner (7). The substitution products described here were minor products compared to those described previously (7). The product, 1 2-o x o-1 3-m e thoxy-9-hy dro xy-trans-10-octadecenoic acid (13-metho, xy-9,12-ketol), needed no further purification; however, the oleoyl ester of the T-ketol required additional TLC isolation.…”

“…The oleoyl ester of 7-ketol, mostly 9-oleoyloxy-12-oxotrans-lO-octadecenoic acid, was obtained from fractions 67-75 after silicic acid chromatography, and it amounted to 6% by wt of substrate used. With a 13-LOOH substrate, the analogous reaction of the c~-ketol substitutes the oleoyl group at C-13 instead of at C-9 with the 7-ketol (7). The proposed mechanism of…”