Metabolism of leukotriene B4 in hepatic microsomes

Leukotriene B4 was metabolized in rat hepatic microsomes to two products. Mass spectral analysis of these two metabolites indicated that the major metabolite was the 20-hydroxy metabolite while the minor metabolite was the 19-hydroxy metabolite. The formation of these metabolites required NADPH and was linear with time (20 min) and protein (1.6 mg/ml). The Km apparent and Vmax for omega hydroxylation of LTB4 was 14 uM and 0.138 nmol/min/mg protein. In contrast, the km and Vmax for omega minus one hydroxylation was 54 uM and 0.093 nmol/min/mg protein. These results suggest that omega and omega minus one hydroxylations of LTB4 may be mediated by different isozymes of hepatic P-450.