Propolypeptide of von Willebrand factor serves as a substrate for factor XIIIa and is cross-linked to laminin.

The propolypeptide of von Willebrand factor (pp-vWF) was found to serve as a substrate for Factor XIIIa (FXIIIa). FXIIIa catalyzed polymerization of pp-vWF as well as the incorporation of monodansylcadaverine and [14C]putrescine into pp-vWF in a Ca(2+)- and time-dependent manner. The amount of putrescine incorporated into pp-vWF was increased as a function of putrescine concentration and reached a maximum of 3 mol/mol of pp-vWF, indicating that there are at least 3 glutamine residues in the pp-vWF molecule responsible for the reaction. 125I-pp-vWF was incubated with FXIIIa in the presence of various adhesive glycoproteins. Laminin, among the proteins tested, specifically formed a large molecular weight complex with 125I-pp-vWF in a Ca(2+)- and time-dependent manner. It was also found that FXIIIa catalyzed polymerization of laminin as well as the incorporation of monodansylca-daverine into laminin. The high molecular weight complexes of 125I-pp-vWF (or 125I-laminin) formed in the presence of laminin (or pp-vWF) were immunoprecipitated with anti-laminin (or anti-pp-vWF) antibodies. Taking all the data together it can be concluded that both pp-vWF and laminin have glutamine and lysine residues responsive to FXIIIa and make copolymers by virtue of FXIIIa.