Localization of estrogen synthetase in the chorionic villus fraction after homogenization of human term placenta.

In previous investigations of human placental estrogen synthetase (aromatase), activity was found in the microsomal and mitochondrial fractions after homogenization and subcellular fractionation of placental tissue in isotonic sucrose. We report here that the majority of the placental aromatase sediments in a much heavier particulate fraction than the microsomal or mitochondrial fractions. After low speed centrifugation of the placental homogenate, only about 20% of the homogenate aromatase activity was measured in the supernatant, the precursor of the microsomal and mitochondrial fractions. Even after extensive homogenization in high speed shearing-type blenders and tight-fitting glass homogenizers the majority of the placental aromatase (more than 70%) consistently sedimented at very low centrifugal forces (100 x g ro 10 min) independent of whether the suspending medium contained up to 1.2M sucrose, or IM NaCl, or 50% glycerol. By selectively separating components of the low speed pellet via a sieving procedure or manual dissection of placental tissue, we found that the majority of the enzyme activity is associated with placental chorionic villus fragments. Several extensively washed preparations of villus fragments with aromatase specific activities similar to that found in placental microsomes were synthesis in the villus aromatase fraction was determined to be 1beta,2beta-H removal which is identical with that by placental microsomes and human ovaries. Evidence for the presence of cytochrome P-450 in the villus fraction was obtained by measuring the carbon monoxide-dithionite difference spectrum.