Leukotriene B4 <o-Hydroxylase in Rat Liver Microsomes: Identification as a Cytochrome P-450 That Catalyzes Prostaglandin A! a>-Hydroxylation, and Participation of Cytochrome W

The a)-hydroxylation of leukotriene B4 (LTBA) 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 w-hydroxylase as a P-450. The P-450 seems to be also responsible for prostaglandin A, (PGA]) a)-hydroxylation, but not for lauric aicd w-hydroxylation. The LTB4 a>-hydroxylation is competitively inhibited by PGA,, but not affected by lauric acid. The K, value for PGA, of 38 /tiM agrees with the Km value for PGA, co-hydroxylation of 40 fM. LTB4 inhibits the PGA, <w-hydroxylation by rat liver microsomes in a competitive manner with the K \ of 43 pM., which is consistent with the K ^ for the LTB4 tu-hydroxylation of 42 ptM. An antiserum raised against rabbit pulmonary PG <o-hydroxylase (P-450p-s) inhibits slightly the w-hydroxylations of LTB4 and PGA,, while it has stronger inhibitory effect on lauric acid a>-hydroxylation. In addition to NADPH-cytochrome P-450 reductase