Characterization of the predominant basic protein in human seminal plasma, one cleavage product of the major seminal vesicle protein.

From liquefied human seminal plasma, we purified the predominant basic protein which appears following liquefaction of coagulated semen. The protein was purified in the presence of di-isopropylfluorophosphate to retard its degradation. Heparin-Sepharose chromatography was followed by gel filtration (Biogel P 60) and by fast performance liquid chromatography on a reversed phase column (C8). The basic protein is a single polypeptide chain with an apparent molecular mass of 12.8 kDa, and has a pI value between that of trypsinogen (9.3) and cytochrome C (10.3). The protein contains no carbohydrate, is rich in histidine, glutamate, and lysine, but is devoid of both cysteine and methionine. The amino-terminal portion of the protein sequence is unique: H N K Q E G R D H D K S K G H F H R V V I H H K G G K A H R G-. A specific rabbit antiserum was raised against the 12.8 kDa basic protein. The protein was found to be unique to seminal plasma among all extracellular fluids examined. Three immunologically related 52 kDa, 71 kDa, and 76 kDa proteins were identified in seminal vesicle secretion when it had been reduced. Prostatic enzyme(s) degraded these proteins to the 12.8 kDa basic protein and several other basic proteins with apparent molecular masses below 18 kDa.