Characterization of Leukotriene B₄‐Omega‐Hydroxylase Activity within Human Polymorphonuclear Granulocytes

Abstract

Human polymorphonuclear granulocytes (PMN) metabolize exogenous [3H]leukotriene B4 (LTB4) into 20-hydroxy- and 20-carboxy-[3H]LTB4. The conversion was enhanced at acidic pH values (pH 6.0-7.0). Sonication of purified PMN and subcellular fractionation by differential centrifugation showed that major LTB4-hydroxylase activity was associated with the microsomal fraction (105,000 g pellet). In contrast to intact cells, LTB4-hydroxylase activity within the microsomal fraction revealed optimal activity at neutral pH and was inhibited by a wide range of divalent cations. There was a strict requirement for the presence of suitable electron donors such as NADPH. Heterocyclic nitrogenous bases, such as imidazole and pyridine, inhibited the LTB4 conversion induced by intact PMN as well as by their microsomes. These observations combined with the spectrophotometric analysis (carbon monoxide dithionite-reduced difference spectrum) supported the assumption that LTB4-hydroxylase resembled a cytochrome P-450 enzyme. The LTB4-hydroxylase within human PMN was not identical with the cytochrome P-450 of rat liver; hepatic microsomes only showed minute conversion of LTB4.