Omega-hydroxylation of lipoxin B4 by human neutrophil microsomes: identification of omega-hydroxy metabolite of lipoxin B4 and catalysis by leukotriene B4 omega-hydroxylase (cytochrome P-450LTB omega).
Lipoxin B4 (LXB4) is metabolized either by human neutrophils or by the neutrophil microsomes to a polar compound on a reverse-phase high-performance liquid chromatography. The metabolite is identified as 20-hydroxy-lipoxin B4 (20-OH-LXB4), a novel member in the arachidonic acid cascade, on the basis of ultraviolet spectrometry and gas chromatography-mass spectrometry. The neutrophil microsomes convert LXB4 to its 20-hydroxy derivative under aerobic condition in the presence of NADPH. The reaction is inhibited by carbon monoxide, an inhibitor of cytochrome P-450 (P-450), and by antibodies raised against NADPH-P-450 reductase. A P-450 is thus involved in the omega-hydroxylation of LXB4. The P-450 appears to be the one responsible for leukotriene B4 (LTB4) omega-hydroxylation, P-450LTB omega, based on the following observations. The formation of 20-OH-LXB4 is inhibited solely by substrates of P-450LTB omega such as LTB4 and leukotriene B5 among various fatty acids including prostaglandins. The order of the inhibitory potencies of these substances on the LXB4 omega-hydroxylation is the same as that of their affinities for LTB4 omega-hydroxylase. LTB4 inhibits the reaction in a competitive manner with the Ki value of 0.2 microM, which agrees with the Km value for the LTB4 omega-hydroxylation (0.3 microM).
Department of Biochemistry, Kyushu University School of Medicine, Fukuoka, Japan.
Y
Y
Mizukami
H
H
Sumimoto
R
R
Isobe
S
S
Minakami
D002384:Catalysis; D002851:Chromatography, High Pressure Liquid; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism*; D000072470:Cytochrome P450 Family 4; D005227:Fatty Acids / Q000494:pharmacology; D006801:Humans; D006893:Hydroxyeicosatetraenoic Acids / Q000378:metabolism*; D006900:Hydroxylation; D007700:Kinetics; D007975:Leukotriene B4 / Q000494:pharmacology; D044045:Lipoxins; D013058:Mass Spectrometry; D008861:Microsomes / Q000378:metabolism*; D006899:Mixed Function Oxygenases / Q000378:metabolism*; D009504:Neutrophils / Q000378:metabolism*; D013056:Spectrophotometry, Ultraviolet
D005227:Fatty Acids; D006893:Hydroxyeicosatetraenoic Acids; D044045:Lipoxins; C081511:20-hydroxylipoxin B4; D007975:Leukotriene B4; D003577:Cytochrome P-450 Enzyme System; C042651:lipoxin B4; D006899:Mixed Function Oxygenases; D000072470:Cytochrome P450 Family 4; C040780:leukotriene B4 20-hydroxylase