title: A study of monooxygenase activity in human placental homogenates: in vitro behaviour towards a number of substrates and inhibitors.
abstract: The in vitro effects of cimetidine, metyrapone, SKF-525A and alpha-naphthoflavone on the monooxygenase activity in human placental tissue have been determined by indirect fluorimetric assay methods in placental homogenates from five maternal smokers. The inhibitor concentrations producing half-maximum inhibition (I50 values) were calculated for the O-deethylation of 7-ethoxycoumarin and 7-ethoxyphenoxazone, and the hydroxylation of 2,5-diphenyloxazole. The results indicate that cimetidine is a weak inhibitor of the placental monooxygenase system, resembling metyrapone and SKF-525A in its effects rather than alpha-naphthoflavone. Characterization of the behaviour of the three substrates towards placental monooxygenase activity indicates a much greater enzymic affinity for 7-ethoxyphenoxazone than for 7-ethoxycoumarin or 2,5-diphenyloxazole.
mesh_terms: D015660:7-Alkoxycoumarin O-Dealkylase; D002927:Cimetidine / Q000494:pharmacology; D005260:Female; D006801:Humans; D006899:Mixed Function Oxygenases / Q000032:analysis; D010080:Oxazoles / Q000378:metabolism; D010105:Oxygenases / Q000032:analysis* / Q000037:antagonists & inhibitors; D010920:Placenta / Q000201:enzymology*; D011247:Pregnancy; D011335:Proadifen / Q000494:pharmacology
chemical_list: D010080:Oxazoles; D002927:Cimetidine; C009012:2,5-diphenyloxazole; D011335:Proadifen; D006899:Mixed Function Oxygenases; D010105:Oxygenases; D015660:7-Alkoxycoumarin O-Dealkylase; C027270:cytochrome P448-dependent mono-oxygenase