Specific cyanylation and cleavage at cysteine-104 human hemoglobin α-chain. A novel approach to the problem of the α-chain tryptic core in the study of haemoglobin variants by ‘fingerprinting’ methods

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Abstract
1. A new approach to the analysis, by “fingerprinting”, of the tryptic core region of human haemoglobin alpha-chain is described. 2. The alpha-chain is cyanylated at its single cysteine residue (alpha104) and then split, by exposure to mild alkali, at the N-peptide bond of the resulting beta-thiocyanoalanine residue. 3. The two cleavage fragments, alpha1-103 and alpha104-141, are separated by gel filtration, and the fragment alpha104-141, which contains all the residues of the alpha-chain tryptic core, is digested with pepsin. 4. Preparative “fingerprints” of these peptic peptides yield eight major peptides, which provide complete sequence information for the whole region alpha104-141. 5. The utility of the method is demonstrated by repeating the determination of the substitution in haemoglobin Hopkins-2, a known alpha-chain core variant in which histidine-alpha112 (G19) is replaced by an aspartic acid residue.