Biochemical homology between rat dorsal prostate and coagulating gland. Purification of a major androgen-induced protein.

The anatomically distinct organs, rat dorsal prostate and coagulating gland, were found to display remarkable homology in protein composition, including two major androgen-dependent secretory proteins, referred to as dorsal proteins I and II. Dorsal protein I has been purified and found to be a dimer composed of two identical subunits with sedimentation coefficient 4.6 S, Stokes radium 32 A, and Mr = 71,000 (62,000 by sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis). This dimer (6.8 S, 46 A, Mr = 150,000) dissociates at high ionic strength and can be partially reconstituted by removal of salt. Dorsal protein I is a basic protein (pI 9) with high lysine content and binds to phosphocellulose but not to DEAE-Sepharose. Schiff's staining shows that it contains carbohydrate. Quantitative rocket immunoelectrophoresis using a rabbit antiserum indicates dorsal protein I is produced only in dorsal prostate and coagulating gland. The protein constitutes approximately 25% of total cytosol protein in both organs, yet makes up on 5% of coagulating gland luminal fluid and ejaculated seminal fluid. It was not detected in the rat dorsal prostate tumor (Dunning R3327H). Dorsal protein II is a larger protein (Mr = 80,000 by SDS gel electrophoresis) with higher carbohydrate content. Under nondenaturing conditions, it has a Stokes radius of > 200 A, corresponding to Mr of > 300,000. Dorsal protein II represents a smaller proportion of total cytosol protein than does dorsal protein I, yet is the predominant protein of coagulating gland fluid. The proteins will be useful probes for studies on androgen regulation of specific gene expression and prostatic secretory mechanisms.