Alpha-carboxyamidation of antral progastrin. Relation to other post-translational modifications.
Using radioimmunoassays for amidated and glycine-extended gastrin before and after trypsin-carboxypeptidase B cleavage and chromatography, alpha-carboxyamidation of porcine antral progastrin has been related to tyrosine-O-sulfation and proteolytic cleavages. Corresponding to the sequence at the proteolysis and amidation site, -Gly-Arg-Arg-, antrum contained three COOH-terminally extended precursor types. The glycine-extended gastrins were present in the highest concentrations (241 +/- 58 pmol/g). The degree of tyrosine-O-sulfation was identical for amidated and precursor gastrins irrespective of component size, whereas the component size differed for glycine-extended and amidated forms. For instance, gastrin-34-Gly constituted 54% of the glycine-extended gastrins, while gastrin-34 comprised 8% of the amidated gastrins. The results indicate that tyrosine-O-sulfation occurs prior to NH2-terminal cleavages, which again precede carboxyamidation; but a significant correlation between tyrosine-O-sulfation and proteolytic cleavages or alpha-carboxy-amidation of antral gastrin could not be demonstrated. Furthermore, our results suggest that the immediate precursor of the principal hormonal form, gastrin-17, is gastrin-17-Gly rather than gastrin-34 as previously believed.
Hilsted
L
L
University Department of Clinical Chemistry, Rigshospitalet, Copenhagen, Denmark.
Rehfeld
J F
JF
D000577:Amides / Q000378:metabolism; D000595:Amino Acid Sequence; D000818:Animals; D043424:Carboxypeptidase B; D002268:Carboxypeptidases / Q000378:metabolism; D005755:Gastrins / Q000032:analysis / Q000378:metabolism*; D008969:Molecular Sequence Data; D011498:Protein Precursors / Q000032:analysis / Q000378:metabolism*; D011499:Protein Processing, Post-Translational; D011863:Radioimmunoassay; D013552:Swine; D014357:Trypsin / Q000378:metabolism; D014443:Tyrosine / Q000378:metabolism
D000577:Amides; D005755:Gastrins; D011498:Protein Precursors; C013706:big gastrin; D014443:Tyrosine; C042873:preprogastrin; D002268:Carboxypeptidases; D043424:Carboxypeptidase B; D014357:Trypsin