The TRH-related peptide pyroglutamyglutamylprolinamide is present in human semen

We have recently identified a novel peptide in the rabbit prostate complex which cross-reacts with an antibody to thyrotrophin-releasing hormone (TRH) and has the structure pGlu-Glu-ProNH2. In the present study, high concentrations of a TRH-related tripeptide and also a polypeptide (10-12 kDa) containing a TRH-immunoreactive peptide at its C-terminus were detected in human semen. The low molecular mass TRH-like peptide and the immunoreactive fragment from the polypeptide were isolated from human semen and shown to have identical structures. Amino acid analysis suggested compositions Glx2, Pro1, and after mild acid hydrolysis, the same sequence, Glu-Glu-Pro, was established for the two peptides. Fast atom bombardment (FAB) mass spectrometry yielded a pseudomolecular ion (M + H)+ of 355.38 which was identical to that of the synthetic peptide pGlu-Glu-ProNH2. The data demonstrate that human semen contains the TRH-like peptide pyroglutamylglutamylprolinamide and also a polypeptide terminating in the sequence Gln-Glu-ProNH2.