A study of the distribution of 7-ethoxycoumarin O-de-ethylase activity in human placental subcellular fractions

Human placental homogenates from maternal smokers and non-smokers were fractionated using differential centrifugation techniques. Yields of the various subfractions were determined and their homogeneity assessed using electron microscopic procedures. The distribution and response of 7-ethoxycoumarin O-de-ethylase activity towards inhibition by dimethylsulphoxide, α-naphthoflavone and 9-hydroxyellipticine inhibitors in the placental subfractions were investigated. The low yield of microsomal protein obtained following differential centrifugation of placental homogenates (2.5±0.2 mg protein per g placenta) highlights the extremely refractory nature of human placental tissue towards homogenization. Enzymic studies showed that the majority (75 per cent) of the original O-de-ethylase activity in homogenates from smokers and non-smokers was to be found in the crude nuclear fraction. The 7-ethoxycoumarin O-de-ethylase activity present in both homogenate and crude nuclear preparations from a maternal smoker was found to be inhibited by both α-naphthoflavone and 9-hydroxyellipticine to a lesser extent than the O-de-ethylase activity which was present in both mitochondrial and microsomal fractions. While this observation suggests the existence of more than one induced O-de-ethylase activity in the human placenta, the possibility that such differences in inhibitory response may be due to other factors (e.g. inhibitor solubility effects) cannot be excluded.