Fibrinogens Kawaguchi and Osaka: An Amino Acid Substitution of Aα Arginine-16 to Cysteine Which Forms an Extra Interchain Disulfide Bridge between the Two Aα Chains1

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Abstract
Structural analyses of fibrinogens from patients with congenital dysfibrinogenemia, designated as fibrinogens Kawaguchi and Osaka, have been performed to identify the difference responsible for the lack of fibrinopeptide A release. For the structural studies, a new strategy was employed. Amino acid sequence analysis of one of the lysyl endopeptidase-peptides isolated from the abnormal fibrinogens indicated that in both fibrinogens, arginine-16 of the Aα chain had been replaced by cysteine. To characterize the chemical nature of the sulfhydryl group of cysteine-16, a tryptic peptide containing cysteine-16 of the Aα chain was prepared from intact fibrinogen Kawaguchi. The amino acid composition and the molecular weight determination of this aberrant peptide revealed that it was a dimeric NH2-terminal peptide corresponding to residues 1–19 derived from the abnormal Aα chain. These results indicate that the half-cystine at position 16 in the abnormal Aα chain forms an intramolecular disulfide bridge with the same residue in the other abnormal Aα chain and that fibrinogen Kawaguchi is a homo dimer composed of two identical abnormal halves.

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