enzymes that cause coagulation in plasma by forming a complex with human prothrombin. Coagulases are produced by certain staphylococcus and yersinia pestis. Staphylococci produce two types of coagulase: Staphylocoagulase, a free coagulase that produces true clotting of plasma, and Staphylococcal clumping factor, a bound coagulase in the cell wall that induces clumping of cells in the presence of fibrinogen.