Hydroxylation of prostaglandins A1 and E1 by liver microsomal monooxygenase. Characteristics of the enzyme system in the guinea pig

D. Kupfer, J. Navarro, D. E. Piccolo

Research output: Contribution to journalArticle

34 Scopus citations

Abstract

Guinea pig liver microsomes in the presence of NADPH catalyzed the hydroxylation of prostaglandin A1 (PGA1) and prostaglandin E1 (PGE1) primarily (>95%) at the ω-1 and to a minor extent (<5%) at the ω position, yielding 19-hydroxy and 20-hydroxy derivatives. The identity of the 19-hydroxy metabolites was established in the form of 19-OH-PGB1 after isolation with the help of high pressure liquid chromatography (HPLC). The isolated product having characteristic UV absorption of PGB1 (λ(max) = 278 nm) was compared with authentic 19-OH-PGB1. The metabolites from PGA1 and PGE1 and authentic 19-OH-PGB1 exhibited identical retention times in HPLC as free acids and as the corresponding methyl esters. The corresponding t-butyldimethylsilyl ethers-methyl esters also exhibited identical retention times in the gas chromatography (GC) and similar fragmentations in GC/mass spectrometry. Both NADPH and NADH supported the hydroxylation of PGA1 and PGE1, NADH being less effective. There was no synergism by NADH of the NADPH-supported hydroxylation. Inhibitors of microsomal monooxygenase such as SKF 525A, metyrapone, nicotinamide, and carbon monoxide inhibited the hydroxylation of PGA1 and PGE1; similarly cytochrome c and antibodies to NADPH-cytochrome c reductase inhibited these reactions, indicating that the hydroxylation of these prostaglandins is catalyzed by a typical monooxygenase system. The kinetic constants for the hydroxylation of PGA1 and PGE1 were determined; the K(m) values were 2.1 x 10-4 M and 1.4 x 10-4 M, respectively. The V(max) values for the two prostaglandins were also similar, being for PGA1 and PGE1, 21.8 and 16.7 nmol/h/mg of protein, respectively.

Original languageEnglish (US)
Pages (from-to)2804-2811
Number of pages8
JournalJournal of Biological Chemistry
Volume253
Issue number8
StatePublished - Jan 1 1978
Externally publishedYes

ASJC Scopus subject areas

  • Biochemistry
  • Molecular Biology
  • Cell Biology

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