Identification of gastrin component I as gastrin-71. The largest possible bioactive progastrin product.
Gastrin component I is the largest hormonally active form of gastrin. In order to determine its structure, we isolated progastrin-derived peptides from normal human antral tissue. A radioimmunoassay specific for sequence 20-25 of human progastrin was developed to monitor the purifications. After four or five steps of reverse-phase chromatography, the peptides were pure and could be identified by a combination of microsequence, amino acid and mass spectral analysis as well as by a library of sequence-specific immunoassays. In addition to intact progastrin 1-80, fragments 1-71, 1-35, 6-35, 20-35, and 20-36 of progastrin were identified. Only the 71-amino-acid peptide contained at its C-terminus the alpha-amidated bioactive site (Trp-Met-Asp-Phe-NH2). This unoheptacontapeptide amide (gastrin-71) corresponds to component I and is the largest possible bioactive product of progastrin. Its structure shows that progastrin is used in its entirety for biosynthesis of active peptides. The occurrence of fragments 6-35, 20-35, and 20-36 demonstrate that antral progastrin is partially cleaved at two monobasic sites (Arg5 and Arg19) in addition to processing at the three C-terminal dibasic sites. The results show that both the N- and C-terminal parts of antral progastrin undergo extensive processing. The results also suggest that progastrin may follow two different processing pathways of which the less trafficked releases gastrin-71.
Rehfeld
J F
JF
Department of Clinical Biochemistry, Rigshospitalet, University of Copenhagen, Denmark.
Johnsen
A H
AH
D000595:Amino Acid Sequence; D002850:Chromatography, Gel; D005753:Gastric Mucosa / Q000737:chemistry*; D005755:Gastrins / Q000737:chemistry* / Q000494:pharmacology; D006801:Humans; D013058:Mass Spectrometry; D008954:Models, Biological; D008969:Molecular Sequence Data; D011498:Protein Precursors / Q000737:chemistry* / Q000494:pharmacology; D011499:Protein Processing, Post-Translational; D011706:Pyloric Antrum / Q000737:chemistry*; D017421:Sequence Analysis
D005755:Gastrins; D011498:Protein Precursors; C013706:big gastrin; C036227:gastrin I