Isolation of a glucagon-containing peptide: primary structure of a possible fragment of proglucagon.

The heterogeneity of crystalline bovine (ox)/porcine glucagon has been examined by gel filtration and ion-exchange chromatography. A strongly basic peptide that reacted well with antibodies to bovine/porcine glucagon was isolated and its primary structure was determined. The amino-acid sequence of the NH(2)-terminal 29 residues of the 4500-dalton peptide is identical with that of intact bovine or porcine glucagon. The remaining eight residues at its COOH-terminus are Lys-Arg-Asn-Asn-Lys-Asn-Ile-Ala. Small amounts of other glucagon-immunoreactive peptides having molecular weights ranging from 3700 to 9000 were also detected in crystals of bovine/porcine glucagon. We propose that the 37-residue peptide is a fragment of bovine or porcine proglucagon.