Leukotriene B4 omega-hydroxylase in rat liver microsomes: identification as a cytochrome P-450 that catalyzes prostaglandin A1 omega-hydroxylation, and participation of cytochrome b5.
The omega-hydroxylation of leukotriene B4 (LTB4) by rat liver microsomes requires NADPH and molecular oxygen, suggesting that the hydroxylation is catalyzed by a cytochrome P-450 (P-450)-linked monooxygenase system. The reaction is inhibited by CO, and the inhibition is reversed by irradiation of light at 450 nm in a light-intensity-dependent manner. The extent of the reversal is strongly dependent on the wavelength of the light used, the 450-nm light is most efficient. The finding provides direct evidence for the identification of the LTB4 omega-hydroxylase as a P-450. The P-450 seems to be also responsible for prostaglandin A1 (PGA1) omega-hydroxylation, but not for lauric acid omega-hydroxylation. The LTB4 omega-hydroxylation is competitively inhibited by PGA1, but not affected by lauric acid. The Ki value for PGA1 of 38 microM agrees with the Km value for PGA1 omega-hydroxylation of 40 microM. LTB4 inhibits the PGA1 omega-hydroxylation by rat liver microsomes in a competitive manner with the Ki of 43 microM, which is consistent with the Km for the LTB4 omega-hydroxylation of 42 microM. An antiserum raised against rabbit pulmonary PG omega-hydroxylase (P-450p-2) inhibits slightly the omega-hydroxylations of LTB4 and PGA1, while it has stronger inhibitory effect on lauric acid omega-hydroxylation. In addition to NADPH-cytochrome P-450 reductase, cytochrome b5 appears to participate in the LTB4 omega-hydroxylating system, since the reaction is inhibited by an antibody raised against the cytochrome b5 as well as one raised against the reductase.
Sumimoto
H
H
Department of Biochemistry, Kyushu University School of Medicine, Fukuoka.
Kusunose
E
E
Gotoh
Y
Y
Kusunose
M
M
Minakami
S
S
D000818:Animals; D065607:Cytochrome P-450 Enzyme Inhibitors; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism*; D000072470:Cytochrome P450 Family 4; D015786:Cytochromes b5 / Q000378:metabolism*; D005227:Fatty Acids / Q000494:pharmacology; D006900:Hydroxylation; D066298:In Vitro Techniques; D007527:Isoenzymes / Q000378:metabolism; D007700:Kinetics; D007975:Leukotriene B4 / Q000378:metabolism / Q000031:analogs & derivatives; D008297:Male; D008862:Microsomes, Liver / Q000201:enzymology*; D006899:Mixed Function Oxygenases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D009251:NADPH-Ferrihemoprotein Reductase / Q000378:metabolism; D010777:Photochemistry; D011453:Prostaglandins / Q000494:pharmacology; D011454:Prostaglandins A / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains
D065607:Cytochrome P-450 Enzyme Inhibitors; D005227:Fatty Acids; D007527:Isoenzymes; D011453:Prostaglandins; D011454:Prostaglandins A; D007975:Leukotriene B4; C031571:5,12,20-trihydroxy-6,8,10,14-eicosatetraenoic acid; D015786:Cytochromes b5; D003577:Cytochrome P-450 Enzyme System; D006899:Mixed Function Oxygenases; D000072470:Cytochrome P450 Family 4; C040780:leukotriene B4 20-hydroxylase; D009251:NADPH-Ferrihemoprotein Reductase