Isolation of vesicles mediating the conversion of 17 beta-estradiol to estrone

The 17 beta-estradiol dehydrogenase of porcine endometrium was found to be localized in specialized particles. Their isolation was achieved by successive partitioning of postmitochondrial supernatants in isopycnic Percoll gradients and on sucrose gradients in a vertical rotor. The purified structures, rich in estradiol dehydrogenase, equilibrate at 1.180 g/ml in sucrose gradients, are on average 150 nm in diameter, have electron-dense cores and are studded with particles of ribosome-like appearance. They do not coequilibrate with enzymic markers for the endoplasmic reticulum (P450 enzymes and RNA), mitochondria, the Golgi apparatus, and lysosomes. The estradiol dehydrogenase activity in the isolated particles was enriched 20-fold from the homogenate.