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J. Biochem, 1990, Vol. 108, No. 2 215-221
© 1990 Japanese Biochemical Society

research-article

Leukotriene B {omega}-Hydroxylase in Rat Liver Microsomes: Identification as a Cytochrome P-450 That Catalyzes Prostaglandin A1 {omega}-Hydroxylation, and Participation of Cytochrome b5

Hideki Sumimoto*, Emi Kusunose**, Yoichi Gotoh*, Masamichi Kusunose**,2 and Shigeki Minakami*

*Department of Biochemistry, Kyushu University School of Medicine Higashi-ku, Fukuoka, FUkUOka 812
**Toneywna Institute for Tuberculosis Research, Osaka City University Medical School Toyonaka, Osaka 560

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 LTB {omega}-hydroxylase as a P-450. The P-450 seems to be also responsible for prostaglandin A, (PGA aj-hydroxylation, but not for laurie aicd {omega}-hydroxylation. The LTB. {omega}-hydroxylation is competitively inhibited by PGAI, but not affected by lauric acid. The K, value for PGAI of 38 M agrees with the X value for PGA {omega}-hydroxylation of 40 µM. LTB inhibits the PGAI {omega}-hydroxylation by rat liver microsomes in a competitive manner with the K, of 43 pM, which is consistent with the K for the LTB {omega}-hydroxylation of 42 µM. An antiserum raised against rabbit pulmonary PG {omega}-hydroxylase (P-450p-2 inhibits slightly the {omega}-hydroxylations of LTB and PGAI, 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 LTB {omega}-hydroxylating system, since the reaction is inhibited by an antibody raised against the cytochrome b as well as one raised against the reductase.

1This work was supported in part by Grants-in-Aid from the Ministry of Education, Science and Culture of Japan.

2Present address: Department of Food Science and Technology, Faculty of Engineering, Fukuyaina University, Fukuyema, Hire shirna 729-02.


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