FUNCTIONAL-CHARACTERIZATION OF A VARIANT PREKALLIKREIN (PK-ZURICH)

The plasma of a 68-year-old man with cross reacting material (CRM)-pos itive prekallikrein (PK) deficiency was studied. PK clotting activity was <0.01 U/ml, and PK antigen was 0.1 U/ml. No circulating anticoagul ant against PK was detectable. The abnormal PK molecule, denoted as pr ekallikrein Zurich, was partially characterized by immunological and f unctional studies on the propositus' plasma. Immunoblotting analysis s howed the abnormal PK being a single chain molecule of the same M(r) ( 80 kDa) as normal PK. Dextran sulfate activation of the propositus' pl asma did not lead to proteolytic cleavage of the variant PK molecule, in contrast to dextran sulfate activation of a mixture of 1 volume nor mal plasma and 9 volumes CRM-negative PK deficient plasma. Agarose gel electrophoresis followed by immunoblotting demonstrated that PK Zuric h was complexed with high molecular weight kininogen similarly to PK i n normal plasma. Incubation of the propositus' plasma with purified be ta-FXIIa resulted in impaired cleavage of PK Zurich when compared with PK hydrolysis in a mixture of 10% normal plasma and 90% CRM-negative PK deficient plasma. Moreover, proteolytically cleaved PK Zurich showe d no enzymatic activity against factor XII and high molecular weight k ininogen. These studies show that the functional defect of prekallikre in Zurich is due to an impaired cleavage by activated factor XII and p robably the lack of enzymatic activity of the cleaved variant molecule .