Reduced cofactor function of human high molecular weight kininogen induced by human plasma kallikrein

Most reports in the literature state that human plasma kallikrein does not destroy the capacity of human high molecular weight kininogen (HMrK) to function as a cofactor in the contact phase activation of factor XII. In the present work preparations of highly purified human plasma kallikrein that showed high plasminogen activator (PGA) activities rapidly reduced the cofactor function of human HMrK. Gel electrophoresis with SDS without reduction showed that all kallikrein preparations tested contained two protein bands, one major band with a Mr of about 83,000, and one weak band with a Mr of 80,000. The main band is probably identical with kallikrein I, which Levison & Tomalin (1982b), using Ac-Pro-Phe-Arg-OMe-HCl as substrate, found to be ten times more active (in terms of kcat/Km) than kallikrein II with Mr 3000 daltons lower. The rate of HMrK destruction in our experiments varied with the kallikrein preparation used, but assays of their hydrolytic activities against benzoyl arginine ethylester (BAEe) or the plasma kallikrein selective tripeptide substrate H-D-Pro-Phe-Arg-pNA (S-2302) did not discriminate between enzyme preparations with different HMrK-destroying capacities. Assay of PGA activities demonstrated a correlation between the level of PGA measured, and the HMrK-destroying capacity.