Purification and distribution of a major protein in rat prostate that binds estramustine, a nitrogen mustard derivative of estradiol-17 beta.

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Abstract
A protein in rat ventral prostate cytosol that binds estramustine [estradiol 3-bis(2-chloroethyl)carbamate] [an antitumor agent] was purified to homogeneity by using chromatography on DEAE-cellulose, Sephadex G-100 (superfine), octyl-Sepharose CL-4B and polyacrylamide gel electrophoresis. The estramustine-binding protein had a MW of 46,000 as estimated by gel filtration. After analysis by polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate, the protein was found to consist of 2 subunits with MW of about 20,000 and 18,000. After reduction of disulfide bridges, the protein was decomposed into 3 components with MW of about 12,000, 11,000 and 8000. Amino acid analysis indicated that the protein is a glycoprotein. Antibodies against the protein were raised in rabbits and a radioimmunoassay was developed for it. The estramustine-binding protein constituted about 18% of the total protein in rat ventral prostate cytosol, was present in the dorsal and lateral lobes of the prostate, and was also detected in the pituitary gland, cerebral cortex, submaxillary gland, thyroid gland, adrenal gland, seminal vesicle, coagulating gland, epididymis and preputial gland of the male rat. In female rats the protein was detected in cerebral cortex. Because the estramustine-ginding protein is predominantly found in the accessory sexual glands of the male rat, it may be of importance for maintaining male fertility.