Human factor V molecule.

(A) Diagram of the organization of the human factor V molecule. The arrows on the top represent activation cleavages by α-thrombin, factor Xa, and RVV-V activator. The arrows at the bottom indicate inactivation cleavages by APC and plasmin. The positions of posttranslational modifications are also shown. (B) Active factor V (factor Va). Following activation by α-thrombin, the active cofactor is a heterodimer composed of a heavy chain divalent cation associated with light chain. The B region of the cofactor is released as 2 fragments. (C) Inactive factor Va (factor Va_i). The upper part shows inactivation of factor Va by APC, resulting in the dissociation of the A2 domain as 2 fragments, A2_N and A2_C. The lower part shows inactivation of factor Va by α-thrombin following cleavage of the heavy chain at Arg643.