Complete sequences of glucagon-like peptide-1 from human and pig small intestine.
In the small intestine, proglucagon is processed into the previously characterized peptide "glicentin" (proglucagon (PG) 1-69) and two smaller peptides showing about 50% homology with glucagon: glucagon-like peptide-1 and -2. It was assumed that the sites of post-translational cleavage in the small intestine of the proglucagon precursor were determined by pairs of basic amino acid residues flanking the two peptides. Earlier studies have shown that synthetic glucagon-like peptide-1 (GLP-1) synthesized according to the proposed structure (proglucagon 71-108 or because residue 108 is Gly, 72-107 amide) had no physiological effects, whereas a truncated from of GLP-1, corresponding to proglucagon 78-107 amide, strongly stimulated insulin secretion and depressed glucagon secretion. To determine the amino acid sequence of the naturally occurring peptide we isolated GLP-1 from human small intestine by hydrophobic, gel permeation, and reverse-phase high performance liquid chromatography. By analysis of composition and sequence it was determined that the peptide corresponded to PG 78-107. By mass spectrometry the molecular mass was determined to be 3295, corresponding to PG 78-107 amide. Furthermore, mass spectrometry of the methyl-esterified peptide showed an increase in mass compatible with the presence of alpha-carboxyl amidation. Thus, the gut-derived insulinotrophic hormone GLP-1 is shown to be PG 78-107 amide.
Orskov
C
C
Department of Clinical Chemistry, Rigshospitalet, Copenhagen, Denmark.
Bersani
M
M
Johnsen
A H
AH
Højrup
P
P
Holst
J J
JJ
D000595:Amino Acid Sequence; D000596:Amino Acids / Q000302:isolation & purification; D000818:Animals; D002851:Chromatography, High Pressure Liquid; D008401:Gas Chromatography-Mass Spectrometry; D005768:Gastrointestinal Hormones / Q000302:isolation & purification* / Q000378:metabolism; D052216:Glucagon-Like Peptide 1; D006031:Glycosylation; D006801:Humans; D007421:Intestine, Small; D008969:Molecular Sequence Data; D010455:Peptides / Q000302:isolation & purification* / Q000378:metabolism; D013552:Swine
D000596:Amino Acids; D005768:Gastrointestinal Hormones; D010455:Peptides; D052216:Glucagon-Like Peptide 1