Involvement of a Complement-Like Factor in the Activation of Blood Protease

Summary The activation of the protease of blood serum or plasma by streptococcal fibrinolysin requires the presence of both a heat-stable and a heat-labile factor. The heat-stable factor is demonstrable in heated human serum, plasma, milk, colostrum, and saliva. Cows’ milk and colostrum also contain the factor. Useful sources of the heat-labile factor include guinea-pig serum, rabbit plasma, duck serum, and chicken serum. The activation of blood protease by streptococcal fibrinolysin is prevented by many reagents that remove or destroy midpiece of complement. Calcium ions seem to be required for the activation.