Newand Rapid Functional Assay for Cl Inhibitor in Human Plasma

c i’ inhibitor (Ci-INH) and a2-macroglobulin (a2M) account for over 90% of the inactivation of purified plasma kallikrein by normal human plasma. The rate of kallikrein inactivation is also dependent on the presence of high molecular weight kininogen (HMWK). which forms a reversible complex with kallikrein protecting the active site of the enzyme against inhibitors. By selectively mactivating a2M with methylamine. and eliminating the protective effect of HMWK by dilution. the inactivation of kallikrein by plasma became almost exclusively dependent on Cl -INH. Functional Ci inhibitor was assessed by measuring the pseudo-first-order rate constant for the inactivation of