Evidence for Intramolecular Cross-Linked Aα·γ Chain Heterodimers in Plasma Fibrinogen

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Abstract
A peptide band of ∼105 kDa migrating near the γ dimer position of disulfide bond reduced human plasma fibrinogen prepared from fresh single donor or outdated plasma was identified by SDS−PAGE. The band, amounting to ∼2% of the total Aα/γ chain population, was thrombin and plasmin sensitive and reacted with antibodies to Aα or γ chains but not with antibodies to Bβ chains, plasminogen, or factor XIII. Amino acid sequencing revealed a double sequence corresponding to that of Aα and γ chains, indicating that the band consists of covalently cross-linked Aα·γ chain heterodimers. Aα·γ heterodimers were identified as a component of monomeric fibrinogen by two-dimensional SDS−PAGE and by SDS−PAGE analysis of the monomer fraction isolated by gel sieving chromatography, thus indicating that Aα·γ heterodimers arise by intramolecular Aα/γ chain cross-linking.