Staphylokinase (SAK) is an amino acidenzyme from Staphylococcus aureus. It is positively regulated by the "agr" gene regulator. It activates plasminogen to form plasmin, which digest fibrin clots. This disrupts the fibrin meshwork which can often form to keep an infection localized.
Staphylokinase also cleaves IgG and complement component C3b, inhibiting phagocytosis.