title: Identification of ubiquinone-50 as the major methylated nonpolar lipid in human monocytes. Regulation of its biosynthesis via methionine-dependent pathways and relationship to superoxide production.
abstract: Human blood monocytes incorporated the methyl group from methionine into their neutral lipids. The major methylated product was identified as ubiquinone-50 in monocytes, lymphocytes, and a variety of human tumor cell lines by several analytical procedures including TLC or high performance liquid chromatography and as ubiquinone-45 in a mouse tumor cell line. Up to three methyl groups were shown to be derived from methionine by mass spectrometry. The rate of synthesis of ubiquinone-50 by monocytes as assessed by measuring labeled methyl group incorporation was shown to be linear over a 3-h period. Degradation of ubiquinone proceeded slowly; 80% of the labeled compound persisted after 18 h. The dependence of ubiquinone-50 synthesis upon methionine concentration was established in monocytes, with an estimated apparent Km for methionine of about 20 microM. The tumor promoter, tetradecanoate phorbol acetate, a potent stimulator of superoxide anion (O2-) production in phagocytic cells, inhibited ubiquinone-50 synthesis at nanomolar concentrations in monocytes, but not in lymphocytes, under conditions where oxidation of methionine takes place. Degradation of the labeled ubiquinone was unaffected. Formylmethionylleucyl-phenylalanine, a chemoattractant peptide which stimulates O2- production in phagocytic cells, also inhibited ubiquinone-50 synthesis. The degree of inhibition by either stimulus was increased when the methionine concentration in the medium was low. These findings demonstrate that in human monocytes ubiquinone-50 biosynthesis is regulable and that methionine concentration modulates both its rate of synthesis and the inhibitory effects of two stimuli of O2- production.
mesh_terms: D000818:Animals; D002460:Cell Line; D002634:Chemotaxis, Leukocyte / Q000187:drug effects; D002855:Chromatography, Thin Layer; D003067:Coenzymes; D006801:Humans; D007700:Kinetics; D008715:Methionine / Q000097:blood*; D008745:Methylation; D009000:Monocytes / Q000378:metabolism*; D009239:N-Formylmethionine / Q000031:analogs & derivatives / Q000494:pharmacology; D009240:N-Formylmethionine Leucyl-Phenylalanine; D009842:Oligopeptides / Q000494:pharmacology; D010100:Oxygen / Q000097:blood*; D013481:Superoxides / Q000097:blood*; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D014316:Tritium; D014451:Ubiquinone / Q000031:analogs & derivatives* / Q000096:biosynthesis / Q000097:blood
chemical_list: D003067:Coenzymes; D009842:Oligopeptides; D014316:Tritium; D013481:Superoxides; D014451:Ubiquinone; D009239:N-Formylmethionine; D009240:N-Formylmethionine Leucyl-Phenylalanine; D008715:Methionine; C024989:coenzyme Q10; D013755:Tetradecanoylphorbol Acetate; D010100:Oxygen