ZINC(II) SELECTIVELY ENHANCES THE INHIBITION OF COAGULATION-FACTOR-XIA BY PROTEASE NEXIN-2 AMYLOID BETA-PROTEIN PRECURSOR

Protease nexin-2 (PN-2) is the secreted isoform of the Alzheimer's Amyloid beta-Protein Precursor (A beta PP) that contains the Kunitz-type protease inhibitor (KPl) domain. PN-2/A beta PP is a potent inhibitor of coagulation factor Xla (FXla) and is secreted in large quantities by activated platelets suggesting a normal function in regulating this protease at sites of vascular injury. In the present study, the effect of Zn2+ on the protease inhibitory properties of PN-2/A beta PP was quantitatively investigated. Zn2+ (1 mu M to 1 mM) had no effect on the inhibition of trypsin or chymotrypsin by PN-2/A beta PP. In contrast, Zn2+ at concentrations >1 mu M increased the inhibition of FXla by PN-2/A beta PP. Enhancement of FXla inhibition was virtually saturated at approximate to 100 mu M Zn2+ resulting in a final K-i approximate to 6.0 x 10(-11) M. Zn2+ had no effect on the inhibition of FXla by a purified, recombinant KPI domain of PN-2/A beta PP indicating that the native protein is required for the potentiation of FXla inhibition. Heparin and Zn2+ were found to further augment each other's ability to stimulate the inhibition of FXla by PN2/A beta PP. Together, these findings suggest that the interaction of Zn2+ with PN-2/A beta PP may be important for optimal inhibition of FXla.