PHOTOAFFINITY-LABELING OF THE PRIMARY FIBRIN POLYMERIZATION SITE - LOCALIZATION OF THE LABEL TO GAMMA-CHAIN TYR-363

Fragment D prepared from human fibrinogen was labeled specifically by photoactivation of the peptide [C-14]Gly-Pro-Arg-N-(4-azido-2-nitrophe nyl)Lys amide. The preparation was freed of excess labeling reagents a nd then reduced and alkylated. The component alpha, beta, and gamma-ch ains were purified by chromatography on carboxymethylcellulose and the radioactivity was found to be restricted to the gamma-chain. Isolated gamma-chains were digested with various endopeptidases, both alone an d in tandem, and the products were fractionated by gradient HPLC. The amino acid compositions of all labeled peptides led to the conclusion that the modification occurs exclusively on gamma-chain Tyr-363.