Identification of the epitope for anti-FXIII-B(2) antibody on FXIII-B. (A) The tryptic fragments of FXIII-B bound to anti-FXIII-B(2) antibody was identified by MALDI-TOF. The numbers above the peaks corresponding to the 2 fragments represent the measured m/z values. A third major peak at m/z 2777.47 could not be identified in the primary structure of FXIII-B. (B) The amino acid sequence of identified fragments and their location in the primary structure of FXIII-B.