Enzymic Nature of the Serum Globulin Permeability Factor

Abstract

THE globulin permeability factors obtainable from the serum of man¹, guinea pig^2,3, rat⁴ and rabbit⁴ appear to be proteases because they are highly active on vascular endothelium—on a molar basis, they are 60–2,000 times as active as histamine, itself a potent permeability factor⁵; and because they are readily inhibited by prior treatment in vitro with the trypsin inhibitors from soya bean, lima bean and bovine pancreas. The action of these inhibitors, however, is apparently very rapid, a mixture of factor and inhibitor only 1 min. old being inactive when injected into the skin of animals with circulating pontamine blue^4,7. Consequently, it is impossible to distinguish inactivation of a protease permeability factor in vitro from inactivation of a protease newly activated in vivo. Moreover, even the best preparations of permeability factors also contain known serum proteases, and so far no enzyme substrate has been found which is hydrolysed by serum fractions in strict proportion to their content of permeability factor.