15-LOX products occur in the membranes of rabbit reticulocytes. Reticulocyte-rich blood cell suspensions were prepared from a rabbit on the seventh day of the bleeding period. The cells were lysed with two vol of distilled water, the membranes were spun down, and the membrane lipids were extracted. After transmethylation with sodium methoxide, the resulting fatty acid methylesters were analyzed by RP-HPLC with a solvent system methanol/water/acetic acid (85/15/0.1, by vol) and a flow rate of 1 mL/min. Upper trace: recording at 210 nm (detection of polyenoic fatty acids), lower trace: recording at 235 nm (detection of oxygenated polyenoic fatty acids. Each trace was normalized with respect to the highest peak of the partial chromatogram. Inset: ultraviolet (UV)-spectrum of the products comigrating with an authentic standard of 13-HODE. In the membranes of rabbit erythrocytes, which were analyzed as controls, these products were not detected (data not shown). 13-HODE, 13-hydroxy-9Z,11E-octadecadienoic acid; LA, linoleic acid; AA, arachidonic acid.