Activation of factor V during intrinsic and extrinsic coagulation. Inhibition by heparin, hirudin and D-Phe-Pro-Arg-Ch2Cl.
The validity of the hypothesis that Factor Xa activates Factor V in heparinized plasma was examined by establishing the temporal relationships between Factor V proteolysis and prothrombin consumption in plasma. Factor V was cleaved into Factor Va heavy chain (approx. 110 kDa) and an intermediate (approx. 230 kDa) 30 s after CaCl2 was added to contact-activated plasma (CAP). The larger fragment was converted into Factor V activation peptide (approx. 150 kDa) and Factor Va light chain (approx. 80 kDa) 15 s later. Heparin (approx. 0.05 microM) delayed Factor V proteolysis in CAP by at least 30 s. On supplementing CAP with 1 nM-Factor Xa or 1 nM-thrombin, Factor V was activated 15 s later. Heparin prolonged by 15 s and 45 s the time required to demonstrate Factor V activation in CAP supplemented with Factor Xa and thrombin respectively. Factor V was activated 20 s after tissue factor and CaCl2 were added to plasma, both in the absence and in the presence of approx. 0.05 microM-heparin. In contrast, hirudin and D-Phe-Pro-Arg-CH2Cl (two thrombin inhibitors more effective than heparin) delayed Factor V activation in this plasma by at least 30 s. The fragments of Factor V obtained in heparinized CAP suggest thrombin escapes inhibition and contributes to Factor V activation in that plasma. Production of Factor Va heavy chain and the 230 kDa Factor V fragment invariably preceded efficient prothrombin activation. These observations suggest that heparin, hirudin and D-Phe-Pro-Arg-CH2Cl delay Factor V activation by inhibiting thrombin. The availability of Factor Xa markedly moderates the ability of heparin to inhibit Factor V activation.
Yang
X J
XJ
Department of Pathology, McMaster University, Hamilton, Ontario, Canada.
Blajchman
M A
MA
Craven
S
S
Smith
L M
LM
Anvari
N
N
Ofosu
F A
FA
D000345:Affinity Labels / Q000494:pharmacology; D001777:Blood Coagulation / Q000187:drug effects; D004789:Enzyme Activation; D005165:Factor V / Q000302:isolation & purification / Q000378:metabolism*; D015951:Factor Xa / Q000378:metabolism; D006493:Heparin / Q000494:pharmacology*; D006629:Hirudins / Q000494:pharmacology*; D006801:Humans; D007700:Kinetics; D009842:Oligopeptides / Q000494:pharmacology*; D013917:Thrombin / Q000378:metabolism; D013925:Thromboplastin / Q000494:pharmacology
D000345:Affinity Labels; D006629:Hirudins; D009842:Oligopeptides; C020924:phenylalanyl-prolyl-arginine methyl chloride; D005165:Factor V; D006493:Heparin; D013925:Thromboplastin; D013917:Thrombin; D015951:Factor Xa