A 75-kDa protein secreted from mouse coagulating gland was purified to homogeneity by a series of isolation steps including ion exchange chromatography on a DEAE-Sephacel column and ion exchange high-performance liquid chromatography on a sulfopropyl column. It was identified to be Type IV transglutaminase (TG(4)), based on the establishment of N-terminal sequences by automated Edman degradation together with partial sequences by MS analysis. Its cross-linking activity was tested on the reduced sample of mouse seminal secretion which contained seven major monomer proteins tentatively designated as SVS I-VII. The enzyme was able to cross-link any of SVS I-III but failed to cross-link the other SVS proteins with a M(r) value less than 14 kDa. SVS I and SVS III showed comparable substrate activity, but were much weaker than SVS II during the TG(4) catalysis.