title: Isolation and characterization of the cyanogen bromide peptides from the B fragment of diphtheria toxin.
abstract: Homogeneous fragment B, obtained through nicking of diphtheria toxin with insoluble trypsin, was cleaved with cyanogen bromide in 70% formic acid. After citraconylation, the cleavage products were separated by gel filtration on Sephadex G--75 and purified by gel filtration, ion-exchange and thin-layer or paper chromatography. Six CNBr peptides were characterized, the composition of which account for the total amino acid content of fragment B. Their apparent molecular weights are: CB 1, 12 000; CB 2, 14 000; CB 3, 8000; CB 4a, 2400; CB 4b, 2200; CB 5, 2200. CB 4a is the NH2--terminal peptide; it contains the cysteine residue of the disulfide bridge linking fragment B to fragment A. CB 3 is the COOH--terminal peptide; it bears the disulfide bridge of fragment B. Characterization of two CNBr--derived overlapping peptides provided the positioning of CB 4b and CB 2 and allowed an alignment of the CNBr peptides of fragment B to be proposed.
mesh_terms: D000595:Amino Acid Sequence; D000596:Amino Acids / Q000032:analysis; D003488:Cyanogen Bromide; D004167:Diphtheria Toxin / Q000032:analysis*; D046911:Macromolecular Substances; D010446:Peptide Fragments / Q000302:isolation & purification
chemical_list: D000596:Amino Acids; D004167:Diphtheria Toxin; D046911:Macromolecular Substances; D010446:Peptide Fragments; D003488:Cyanogen Bromide