Studies on the prekallikrein (kallikreinogen)--kallikrein enzyme system of human plasma. II. Evidence relating the kaolin-activated arginine esterase to plasma kallikrein.

Evidence is presented in this paper that the kaolin-activated arginine esterase of plasma is related to plasma kallikrein activity. Such a relationship is based on studies that (1) establish a constant ratio of esterase activity on various synthetic substrates for the kaolin-activated arginine esterase, purified kallikrein(s), and preparations obtained during the fractionation procedure; (2) exclude other known plasma and tissue arginine esterases; (3) confirm the requirement for factor XII in the activation of the enzyme precursor; and (4) show similarities in behavior between the plasma esterase and purified kallikrein(s) toward a variety of inhibitors. Based on this probable identification, evidence is provided that the concentration of active factor XII determines the rate of activation of plasma kallikreinogen, and that the activation may be blocked by polybrene. Once activated, plasma kallikrein is rapidly inactivated by the naturally occurring plasma inhibitor, but the inhibition is incomplete. Acid or chloroform treatment of plasma rapidly inactivates the plasma inhibitor without affecting the concentration of plasma kallikreinogen. Another plasma arginine esterase with properties suggestive of permeability factor is activated by factor XII in the presence of synthetic substrates, but only at low ionic strength. The data suggest that this enzyme is closely related to plasma kallikrein and that it arises from a common precursor.