Biochemical characterization of hepatic microsomal leukotriene B4 hydroxylases

J Biol Chem. 1987 Feb 5;262(4):1590-5.

Abstract

omega-Hydroxylation of leukotriene B4 (LTB4) has been reported in human and rodent polymorphonuclear leukocytes; preliminary information indicates that this metabolism is cytochrome P-450 dependent. Therefore, these studies were initiated to characterize the cytochrome P-450-dependent metabolism of LTB4 in other tissues. LTB4 was metabolized by rat hepatic microsomes to two products, 20-hydroxy(omega)-LTB4 and 19-hydroxy(omega-1)-LTB4. The formation of these metabolites was both oxygen and NADPH dependent indicating that a monooxygenase(s) was responsible for these reactions. The apparent Km and Vmax for LTB4 omega-hydroxylase were 40.28 microM and 1202 pmol/min/mg of protein, respectively. In contrast, the apparent Km and Vmax for LTB4 (omega-1)-hydroxylase were 61.52 microM and 73.50 pmol/min/mg of protein, respectively. Both LTB4 omega- and (omega-1)-hydroxylases were inhibited by metyrapone in a concentration-dependent fashion. However, SK&F 525A inhibited LTB4 (omega-1)- but not omega-hydroxylase. In contrast, alpha-naphthoflavone decreased LTB4 omega- but not (omega-1)-hydroxylase activities. The differences in the Km apparent for substrate as well as the differential inhibition by inhibitors of cytochrome P-450 suggest that the omega- and (omega-1)-hydroxylations of LTB4 in hepatic microsomes are mediated by different isozymes of P-450. Furthermore, several additional characteristics of LTB4 hydroxylases indicate that these isozymes of P-450 may be different from those which catalyze similar reactions on medium-chain fatty acids, such as laurate and prostaglandins.

MeSH terms

  • Animals
  • Benzoflavones / pharmacology
  • Cytochrome P-450 Enzyme System / metabolism
  • Cytochrome P450 Family 4
  • Kinetics
  • Leukotriene B4 / metabolism*
  • Male
  • Mass Spectrometry
  • Methylcholanthrene / pharmacology
  • Metyrapone / pharmacology
  • Microsomes, Liver / enzymology*
  • Mixed Function Oxygenases / metabolism*
  • Phenobarbital / pharmacology
  • Proadifen / pharmacology
  • Pyrimidines / pharmacology
  • Rats
  • Rats, Inbred F344
  • Temperature

Substances

  • Benzoflavones
  • Pyrimidines
  • Leukotriene B4
  • Methylcholanthrene
  • alpha-naphthoflavone
  • pirinixic acid
  • Cytochrome P-450 Enzyme System
  • Proadifen
  • Mixed Function Oxygenases
  • Cytochrome P450 Family 4
  • leukotriene B4 20-hydroxylase
  • Phenobarbital
  • Metyrapone