Identification of the polypeptide chains involved in the cross-linking of fibrin.

The stabilization of fibrin clots by activated factor XIII involves two different sets of cross-linked chains. In one case (type I) two gamma-chains are linked to each other, indicating that gamma-chains have both donor (suitable lysyl-) and acceptor (suitable glutaminyl-) functions. A second system (type II) consists of a gamma-chain linked to an alpha-chain. Experiments with a substitute donor (glycine ethylester) indicate that only gamma-chains have enzyme-accessible acceptor sites, suggesting that alpha-chain participation is limited to lysyl side chains. A model molecular arrangement for fibrin has been suggested which accommodates all the data.