Characterization of cofactor activities of PZ-PC chimeric proteins. (A) Comparison of the ability of PZ and PZ-PC chimeras to accelerate the inhibition of 0.5nM factor Xa by 40nM plasma ZPI in the presence of phospholipid (15μM) and Ca²⁺ (4mM). Reactions were initiated by adding ZPI last and were allowed to proceed for 60 seconds before measuring residual factor Xa activity by coagulation assay. Reactions initiated with factor Xa showed similar relative ZPI reactivities (not shown). (B) Analysis of the binding of ZPI to the recombinant forms of PZ as assessed in a microtiter-plate assay described in “Characterization of PZ/PC chimeric proteins.”