Two strains of Group A streptococci have been shown to produce streptokinases with different physical and immunologic characteristics. These streptokinases have been designated SK-A and SK-B. Examination of additional strains of Group A streptococci has indicated that SK-A is the more commonly encountered streptokinase.
Studies comparing the two Group A streptokinases with streptokinase of Group C origin have indicated that the latter streptokinase is intermediate between SK-A and SK-B in regard to its electrophoretic mobility. Immunological data suggest that the Group C streptokinase differs from SK-B but is closely related to SK-A.