Fibrinoligase-catalyzed cross-linking of myosin from platelet and skeletal muscle.

Fibrinoligase (thrombin- and calcium-activated Factor XIII) from human plasma catalyzes the incorporation of dansylcadaverine and ¹⁴C]putrescine into myosin, prepared from either human platelets or rabbit skeletal muscle. At least 9 mol of amine is incorporated per mole of myosin of either type when the enzyme is used under saturating conditions. Both heavy and light chains of the platelet and muscle myosins incorporate dansylcadaverine and ¹⁴C]putrescine. However, in quantitative terms, the incorporation into the light chains of either type is much less than into the heavy chains. Profound fluorescent changes occurred when dansylcadaverine was bound to myosin. Highly cross-linked platelet and muscle myosin polymers form in the absence of added amines, indicating the presence of both acceptor and donor sites. ATPase activity was not altered by cross-linking of 50–60% of myosin. The nature of the cross-link in myosin was found to be a γ-glutamyl-?-lysine bond, with an average of 19 mol of dipeptide per mole of platelet myosin.