Factor IXa inhibition by protease nexin-2/amyloid beta-protein precursor on phospholipid vesicles and cell membranes.
Protease nexin-2/amyloid beta-protein precursor (PN-2/A beta PP) is a Kunitz-type protease inhibitor which has been shown to be a tight-binding inhibitor of enzymes, factors XIa and IXa (FIXa), suggesting a role for this protein in hemostasis. Since coagulant reactions are modulated on biologic surfaces, we investigated how 25:75 (mol/mol) phosphatidylserine/phosphatidylcholine vesicles (PSPC), thrombin-activated platelets, or umbilical vein endothelial cells influence inactivation of FIXa by PN-2/A beta PP. The Km of human or porcine FIXa activation of human factor X in the presence of PSPC, activated platelets, or endothelial cells in the absence or presence of thrombin-activated factor VIII (FVIIIa) was similar, (0.05-0.39 microM). The presence of FVIIIa increased the catalytic efficiency (kcat/Km ratio) of human and porcine factor IXa's activation of factor X 4952-406-fold, respectively. In the presence of PSPC, the Ki of human and porcine FIXa inhibition by PN-2/A beta PP was Ki = 1.9 x 10(-9) M and 5.8 x 10(-9) M, respectively. After the addition of FVIIIa to the reaction, the Ki for both human and porcine FIXa inhibition by PN-2/A beta PP on PSPC increased 13- and 4-fold to Ki = 2.5 x 10(-8) M and 2.4 x 10(-8) M, respectively. These Ki for inhibition of human FIXa on phospholipid vesicles by PN-2/A beta PP were similar when factor X activation was measured by chromogenic or activation peptide release assays. FVIIIa reduced the inhibition of FIXa by PN-2/A beta PP only in the presence of PSPC.(ABSTRACT TRUNCATED AT 250 WORDS)
Schmaier
A H
AH
Department of Internal Medicine, University of Michigan, Ann Arbor 48109-0724.
Dahl
L D
LD
Hasan
A A
AA
Cines
D B
DB
Bauer
K A
KA
Van Nostrand
W E
WE
D016564:Amyloid beta-Protein Precursor / Q000494:pharmacology*; D000818:Animals; D001792:Blood Platelets / Q000378:metabolism; D002352:Carrier Proteins / Q000494:pharmacology*; D002462:Cell Membrane / Q000201:enzymology*; D004789:Enzyme Activation; D015949:Factor IXa / Q000037:antagonists & inhibitors*; D015944:Factor VIIIa / Q000378:metabolism; D005170:Factor X / Q000378:metabolism; D006801:Humans; D007700:Kinetics; D010713:Phosphatidylcholines / Q000378:metabolism; D010718:Phosphatidylserines / Q000378:metabolism; D010743:Phospholipids / Q000378:metabolism*; D058255:Protease Nexins; D011956:Receptors, Cell Surface; D013552:Swine
C545487:APP protein, human; D016564:Amyloid beta-Protein Precursor; D002352:Carrier Proteins; D010713:Phosphatidylcholines; D010718:Phosphatidylserines; D010743:Phospholipids; D058255:Protease Nexins; D011956:Receptors, Cell Surface; D015944:Factor VIIIa; D005170:Factor X; D015949:Factor IXa