Microsomal proteins from human fetal livers and mid-gestational and term placentas were stained for heme in an attempt to detect multiple forms of cytochrome P-450. In fetal liver microsomes five protein bands staining for heme in the mol. wt region 46,000-60,000 were found. In the placentas two bands were seen in the region 46,000-52,000. Fetal liver and placental microsomes were assayed for metabolism of benzo[a]pyrene (B[a]P) and 7-ethoxyresorufin (7-EOR). The B[a]P metabolites were separated using high performance liquid chromatography. Following incubations with fetal liver microsomes, in general only phenols were detectable, while after incubations with mid-gestational as well as term placentas from smoking women, the 9,10-, 4,5- and 7,8-dihydrodiols were also formed. No quinones were detected. Placental microsomes from non-smoking women did not catalyse the formation of B[a]P metabolites. The 7-EOR O-de-ethylase activity was in the same range (2-5 pmol/min · mg microsomal protein) in the fetal livers as in the mid-gestational placentas. The activities were somewhat higher in the placentas originating from smokers. No correlation between enzymatic activities in vitro and intensity of any specific protein band was observed for the fetal livers or placentas studied.
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