title: Isolation and identification of N-terminally extended forms of 5-oxoprolylglutamylprolinamide (Glp-Glu-Pro-NH2), a thyrotropin-releasing-hormone (TRH)-like peptide present in human semen.
abstract: N-terminally extended forms of 5-oxoprolylglutamylprolinamide (Glp-Glu-Pro-NH2), a thyrotropin-releasing-hormone(TRH)-like peptide associated with the male reproductive system, were isolated from human semen by gel exclusion on Sephadex G50, ion-exchange chromatography on SP-Sephade C25 and QAE-Sephadex A25, and by HPLC. The peptides were located by trypsin-catalysed release of their C-terminal fragments which were detected by RIA with a TRH-specific antibody. A series of overlapping peptides containing 16, 18, 22 and 25 residues was obtained in homogeneous form and their sequences were determined by automatic Edman degradation. The peptides all terminated in -Lys-Gln-Glu-Pro-NH2 and were found to correspond to sequences occurring between residues 350-374 of semenogelin, a protein present in human semen. In semenogelin, however, the Gln-Glu-Pro sequence is followed by tryptophan and not glycine which is normally essential for formation of the C-terminal amide group. Model experiments with the synthetic peptide Glp-Glu-Pro-Trp showed that under a range of experimental conditions the tetrapeptide did not undergo conversion to Glp-Glu-Pro-NH2. This would indicate that the tripeptide and its extended forms are generated from a precursor that is related to semenogelin but in which Trp375 is replaced by glycine.
authors.affiliation: National Institute for Medical Research, London, England.
authors.forename: Z
authors.initials: Z
authors.lastname: Khan
authors.forename: D G
authors.initials: DG
authors.lastname: Smyth
mesh_terms: D000595:Amino Acid Sequence; D006801:Humans; D008297:Male; D008969:Molecular Sequence Data; D009842:Oligopeptides / Q000737:chemistry / Q000276:immunology / Q000302:isolation & purification*; D011761:Pyrrolidonecarboxylic Acid / Q000031:analogs & derivatives; D012661:Semen / Q000737:chemistry*; D013973:Thyrotropin-Releasing Hormone / Q000737:chemistry / Q000276:immunology / Q000302:isolation & purification* / Q000031:analogs & derivatives
chemical_list: D009842:Oligopeptides; D013973:Thyrotropin-Releasing Hormone; C059697:pyroglutamyl-glutamyl-proline amide; D011761:Pyrrolidonecarboxylic Acid