In the absence of FXIII-A₂, FXIII-B₂ coprecipitates with plasma fibrinogen. Fibrinogen was precipitated from (A) F13a^+/+, F13a^+/−, or F13a^−/− mouse plasma, (B) FXIII-depleted human plasma reconstituted with rFXIII-B₂, or (C) afibrinogenemic mouse plasma using glycine. Panels show representative western blots for fibrinogen (Fgn), FXIII-A, and FXIII-B in the initial plasma (I), pellet (P), or supernatant (S) under reducing (Fgn) or nonreducing (FXIII-A, FXIII-B) conditions. Note in panel A, plasma albumin in I and S samples causes the Aα-chain to migrate faster than in the P samples. Blots are representative of N = 3 experiments with mouse plasmas and N = 2 experiments with human plasma.