Monoclonal Antibody to Noncatalytic Subunit of Bovine Plasma Factor XIII: Selective Isolation of Catalytic Subunit

Abstract

Plasma Factor XIII is a zymogen of plasma transglutaminase (EC 2.3.2.13), which is responsible for the intermolecular crosslinking of fibrin molecules during blood clotting. The factor is a tetramer (a₂b₂) comprising catalytic (a₂) and noncatalytic (b₂) subunits. By fusing mouse myeloma cells with spleen cells of a mouse immunized with Factor XIII protein that was partly purified from bovine plasma, we generated a hybridoma clone (A2) that synthesized a monoclonal antibody against bovine plasma Factor XIII. The subclass of IgG produced by clone A2 was IgG_2a. The monoclonal antibody was not cross-reactive with human placental Factor XIII or guinea pig liver transglutaminase. Experiments with a monoclonal-antibody immunoadsorbent column indicated that the monoclonal antibody recognized an epitope on the noncatalytic subunit, and that bovine plasma Factor XIII also dissociated into catalytic and noncatalytic subunits in the presence of a high concentration of Ca²⁺, as human plasma Factor XIII does. The catalytic subunits had catalytic properties similar to those of Factor XIII activated by thrombin. The immunoadsorbent column provided a one-step purification procedure that isolated the catalytic subunit of bovine plasma Factor XIII from plasma with a high yield. This simple method for isolation of the catalytic subunit will make it possible to use plasma transglutaminase in applied enzymology.