(A) Illustration of the active site in the core domain of factor XIII A subunit. Side chains of active site residues Cys314, His373, Asp396, and Trp279, Ser340, His342, Asp343, Asp345, Trp370, Thr398, and Gln400 are shown along with the side chain of Asn344, which is deleted in the patient studied here. (B) As for Fig8A but showing a possible configuration for the mutant enzyme. Asp343 has a completely different orientation that is expected to be detrimental for enzyme activity.