Open AccessIsolation and identification of N ‐terminally extended forms of 5‐oxoprolylglutamylprolinamide (Glp‐Glu‐Pro‐NH 2 ), a thyrotropin‐releasing‐hormone(TRH)‐like peptide present in human semen
Author(s) -
KHAN Zeena,
SMYTH Derek G.
Publication year - 1993
Publication title -
european journal of biochemistry
Language(s) - English
Resource type - Journals
eISSN - 1432-1033
pISSN - 0014-2956
DOI - 10.1111/j.1432-1033.1993.tb17629.x
Subject(s) - peptide , sephadex , biochemistry , peptide sequence , tripeptide , tetrapeptide , edman degradation , trypsin , thyrotropin releasing hormone , chemistry , biology , enzyme , hormone , gene
N‐terminally extended forms of 5‐oxoprolylglutamylprolinamide (Glp‐Glu‐Pro‐NH 2 ), 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‐NH 2 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‐NH 2 . 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.