Metabolic profile of linoleic acid in stored apples: Formation of 13(R)-hydroxy-9(Z),11(E)-octadecadienoic acid

During our ongoing project on the biosynthesis of R-(+)-octane-1,3-diol the metabolism of linoleic acid was investigated in stored apples after inject ion of [1-C-14]-, [9, 10, 12, 13-H-3]-, C-13(18)- and unlabeled substrates. After different incubation periods the products were analyzed by gas chrom atography-mass spectroscopy (MS), high-performance liquid chromatography-MS /MS, and HPLC-radiodetection. Water-soluble compounds and CO2, were the maj or products whereas 13(R)-hydroxy- and 13-keto-9(Z), 11(E)-octadecadienoic acid, 9(S)-hydroxy- and 9-keto-10(E), 12(Z)-octadecadienoic acid, and the s tereoisomers of the 9, 10, 13- and 9, 12, 13-trihydroxyoctadecenoic acids w ere identified as the major metabolites found in the diethyl ether extracts . Hydroperoxides were not detected. The ratio of 9/13-hydroxy- and 9/13-ket o-octadecadienoic acid was 1:4 and 1:10, respectively. Chiral phase HPLC of the methyl ester derivatives showed enantiomeric excesses of 75% (R) and 6 5 % (S) for 13-hydroxy-9(Z),11 (E)-octadecadienoic acid and 9-hydroxy-10(E) ,12(2)-octadecadienoic acid, respectively. Enzymatically active homogenates from apples were able to convert unlabeled linoleic acid into the metaboli tes. Radiotracer experiments showed that the transformation products of lin oleic acid were converted into (R)-octane-1,3-diol. 13(R)-Hydroxy-9(2),11 ( E)-octadecadienoic acid is probably formed in stored apples from 13-hydrope roxy-9(Z), 11(E)-octadecadienoic acid. It is possible that the S-enantiomer of the hydroperoxide is primarily degraded by enzymatic side reactions, re sulting in an enrichment of the R-enantiomer and thus leading to the format ion of 13(R)-hydroxy-9(Z), 11 (E)-octadecadienoic acid.