LC-MS analysis of products generated by incubation of linoleic acid (LA) and yeast cell extracts of Nb-9-LOX (LOX) with or without cysteine (cys). (A) Total ion chromatogram (TIC) and ion traces m/z 319, 335, and 279; 9-HOD, 9-HPOD and linoleic acid were detected by monitoring m/z 319 [M+Na]+, 335 [M+Na]+ and 279 [M-H]-, respectively. 9-HOD and 9-HPOD show almost identical retention times but can clearly be distinguished by their MS and MS/MS data. (B) MS/MS spectrum of reference compound linoleic acid (m/z 279 → 261, negative mode). (C) MS/MS spectum of product 9-HOD (m/z 319 → 301, positive mode) formed from the reaction LOX+LA+cys from (A). (D) MS/MS spectum of product 9-HPOD (m/z 335 → 195, positive mode) formed from the reaction LOX+LA from (A).