title: The induction of benzo[a]pyrene-3-mono-oxygenase by singlet oxygen in liver cell culture is mediated by oxidation products of histidine.
abstract: The photochemical generation of excited states of oxygen by the mild illumination of culture medium containing 15 microM riboflavin results in a typical induction of benzo[a]pyrene-3-mono-oxygenase in cell lines derived from liver. However, the induction of the mono-oxygenase is not due to an excited state of oxygen directly activating the inducing mechanism inside the cell but is due to the oxidation of a component of the culture medium forming a stable inducer. The present work unequivocably shows that the component oxidised is histidine. The mild illumination of culture medium containing riboflavin therefore converts a physiological component of the medium which is not normally an inducer of the mono-oxygenase into a compound which is as effective an inducer as the classical inducer. The finding that singlet oxygen will oxidise a cell constituent into a powerful inducer is compatible with the hypothesis that excited states of oxygen and their oxidation products may play a central role in the induction of cytochrome P-450 and associated enzyme activities by many chemically unrelated inducers.
mesh_terms: D000596:Amino Acids / Q000378:metabolism; D000818:Animals; D001189:Aryl Hydrocarbon Hydroxylases / Q000096:biosynthesis*; D001579:Benzopyrene Hydroxylase / Q000096:biosynthesis*; D002478:Cells, Cultured; D004790:Enzyme Induction; D006639:Histidine / Q000378:metabolism*; D008027:Light; D008099:Liver / Q000201:enzymology*; D010100:Oxygen; D010777:Photochemistry; D051381:Rats; D012256:Riboflavin
chemical_list: D000596:Amino Acids; D006639:Histidine; D001579:Benzopyrene Hydroxylase; D001189:Aryl Hydrocarbon Hydroxylases; D010100:Oxygen; D012256:Riboflavin