Purification and characterization of a steroid-binding sialoglycoprotein from rat ventral prostate.

An androgen-dependent sialoglycoprotein was purified from the secretion of rat ventral prostate by chromatofocusing and DEAE-Sepharose column chromatography. It showed a native molecular weight of 47,000 and consisted of two dissimilar subunits with molecular weights of 20,000 and 18,000. However, each subunit contained a common peptide with molecular weight of 16,000. It also contained 442 +/- 62 micrograms sialic acids per milligram protein and bound pregnenolone with a binding affinity of 1.2 microM-1. Its amino acid composition was similar to those of other known prostatic steroid-binding proteins. Hence, we propose that it is the sialylated form of rat prostatic steroid-binding protein.