Mechanisms of leukotriene formation: hemoglobin-catalyzed transformation of 15-HPETE into 8,15-DiHETE and 14,15-DiHETE isomers

Four isomers of 8,15-diHETE as well as 14,15-diHETEs are isolated and characterized after exposure of 15-HPETE to hemoglobin. It is found that 83% of the C-8 oxygen atoms in 8(R), 15(S)-diHETE and 8(S), 15(S)-diHETE, and 41% of the C-8 oxygen atoms in 8(R), 15(S)-11Z-diHETE and 8(S), 15(S)-11Z-diHETE are derived from H2(18)O. These results suggest that hemoglobin catalyzes the transformation of 15-HPETE into these products via a free radical process, possibly involving the intermediacy of 14,15-LTA. Intact human leukocytes contain a distinct enzyme system for catalyzing the conversion of 15-HPETE into 14,15-LTA. This enzyme activity is inhibited by ETYA and is rapidly denatured upon homogenization of the intact leukocytes.