The membrane-bound 17β-estradiol dehydrogenase of porcine endometrial cells: purification, characterization and subcellular localization

The membrane-bound 17β-estradiol dehydrogenase of porcine endometrial cells was purified to homogeneity as judged by SDS-PAGE and silver staining of a single 32 kD band. A second, more hydrophobic product of the purification protocol contained additional bands at 45 and 80 kD. The 17β-estradiol dehydrogenase activities of both products exceeded those for 17-one reduction by more than 260-fold. Activities of 3α-, 3β- and 20α-dehydrogenases were absent in either fraction. Polyclonal and monoclonal antibodies raised against the 32 kD protein and the more hydrophobic product precipitated the enzymatic activity and reacted with the 32 and 80 kD bands, but not with the 45 kD band in Western blots. The subcellular localization of the enzyme was studied in sections of intact cells and of isolated organelles using gold sol coated with F(ab')₂ fragments of monoclonal antibody F1. Gold particles were found exclusively over cytoplasmic vesicles of 120-150 nm diameter with electron-dense contents.

Purification and properties of oestradiol 17 beta-dehydrogenase extracted from cytoplasmic vesicles of porcine endometrial cells

Porcine endometrial oestradiol-17 beta dehydrogenase was solubilized from the particulate fraction of homogenates sedimenting between 1200 g and 10,000 g by treatment with 0.4% Brij 35 in neutral buffers. The extracts were processed by successive passage through DEAE-Sepharose, Amberlyte XAD-2 and Blue-Sepharose, and the enzyme was collected from the washed affinity matrix at 0.8 M of a 0-2 M-KCl gradient. A genuine oestrone reductase was eluted at 1.9 M-KCl. The dehydrogenase pool was resolved by butyl-Sepharose chromatography into a major (80%) peak (EDHM) eluted at 0.8 M-(NH4)2SO4 and a very hydrophobic fraction (VHF) recovered at 0.1 M. EDHM was further purified by filtration through Sephadex G-200 and cation-exchange chromatography on Mono S. Sephacryl 300 was used for VHF followed by Mono S. Enrichments from the homogenate amounted to 1074-fold for EDHM and 632-fold for VHF. A single silver-stained band at 32 kDa is seen on SDS/PAGE of EDHM, and VHF contains additional bands at 45 and 80 kDa. Polyclonal antibodies (G436) raised against EDHM and the monoclonal antibody F1 raised against VHF recognize the single 32 kDa band in EDHM and both the 32 kDa and 80 kDa bands in composite VHF. The 45 kDa band of VHF reacts with neither. Monoclonal antibody W1 raised against EDHM only recognizes the 32 kDa peptide of EDHM and VHF. The specific activity for oestradiol oxidation amounts to 4081 mu-units/mg for EDHM and to 2402 mu-units/mg for VHF. Both possess a minimal (1/260) endogenous reductase activity and are devoid of 3 beta, 3 alpha- and 20 alpha-dehydrogenases. We consider EDHM to be authentic oestradiol-17 beta dehydrogenase of porcine endometrium. The composite VHF could reflect the situation of the enzyme in vivo or result from aggregations occurring during processing.

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.

Assignment of estradiol-17 beta dehydrogenase and of estrone reductase to cytoplasmic structures of porcine endometrium cells

Homogenates of porcine endometrium contain substantial activity for the dehydrogenation of estradiol-17 beta but little for estrone reduction. Both activities are associated with cytoplasmic structures. The dehydrogenase is characterized by a pH 7.7 optimum, Km 2.2 x 10(-7) mol/l for estradiol and Km 4.4 x 10(-5) mol/l for the cosubstrate NAD+. The corresponding figures for the reductase are pH 6.6, Km 1.1 x 10(-6) mol/l for estrone and Km 2.1 x 10(-5) mol/l for the cosubstrate NADPH. The (mitochondrial/lysosomal) 17,000 x g particulate fraction contains a 52-fold higher dehydrogenase than reductase activity. The (microsomal) 200,000 x g particulate fraction is only 16-fold richer in dehydrogenase. Isopycnic centrifugations of the two fractions in Percoll gradients reveal that estrone reductase and the coequilibrating marker enzyme cytochrome c reductase occur in constant proportions, whereas the dehydrogenase/cytochrome c reductase ratios are different. Both, the kinetic data and the structural assignments speak in favour of individual enzymes catalyzing the dehydrogenation of estradiol and the reduction of estrone. All gradient fractions exhibiting dehydrogenase activity feature small, electrodense vesicles of 0.15-0.20 microns in diameter as a common structural element which might harbour the dehydrogenase.

Harvesting and separation of two populations of lysosomes from porcine endometrium

The lysosomes present in homogenates of porcine endometrium epithelium equilibrate in two density regions of Percoll gradients. Patterns with varying proportions between high and low density peaks are observed, when aliquots of a tissue sample are processed with different all-glass Potter-Elvejhem homogenizers. The described constant-tolerance shearing device (CTSD), in contrast, provides homogenate fractions with higher latencies and steady distribution patterns. They are characteristic for each of the six lysosomal markers and the six other structure-bound enzymes measured in gradient fractions of the particulate matter harvested between 600g and 17,000g. The 17,000g sediments of CTSD homogenates contain more than 40% of the total lysosomal enzymatic activities. Recoveries from Percoll gradients are between 93 and 101%. Enrichments in the high density region range from 35-fold (beta-glucosidase) to 82-fold (acid ribonuclease). Both lysosomal populations exhibit latencies between 89 and 94%. Our results indicate that light lysosomes can be artificially generated by inappropriate homogenization, which should be considered in experiments on the formation and maturation of lysosomes.

A study of the freezing of water in human uterine muscle by proton magnetic resonance

Human uterine muscle and its nuclear fractions have been studied by means of nuclear magnetic resonance at temperatures from 300 degrees K to 143 degrees K. Different proton populations have been detected above and below the freezing point. On this basis it is suggested that the freezing of water in uterine muscle starts at the cell nuclei.