Gln506-factor V (FV) was purified from plasma of an individual homozygous for an Arg506Gln mutation in FV that is associated with activated protein C (APC) resistance. Purified Gln506-FV, as well as Gln506-FVa generated by either thrombin or FXa, conveyed APC resistance to FV-deficient plasma in coagulation assays. Clotting assay studies also suggested that APC resistance does not involve any abnormality in FV-APC-cofactor activity. In purified reaction mixtures, Gln506-FVa in comparison to normal FVa showed reduced susceptibility to APC, because it was inactivated approximately 10-fold slower than normal Arg506-FVa. It was previously reported that inactivation of normal FVa by APC involves an initial cleavage at Arg506 followed by phospholipid-dependent cleavage at Arg306. Immunoblot and amino acid sequence analyses showed that the 102-kD heavy chain of Gln506-FVa was cleaved at Arg306 during inactivation by APC in a phospholipid-dependent reaction. This reduced but measurable susceptibility of Gln506-FVa to APC inactivation may help explain why APC resistance is a mild risk factor for thrombosis because APC can inactivate both normal FVa and variant Gln506-FVa. In summary, this study shows that purified Gln506-FV can account for APC resistance of plasma because Gln506-FVa, whether generated by thrombin or FXa, is relatively resistant to APC.
ARTICLES|
June 15, 1995
Activated protein C resistance: molecular mechanisms based on studies using purified Gln506-factor V
MJ Heeb,
MJ Heeb
Department of Molecular and Experimental Medicine, Scripps Research Institute, La Jolla, CA 92037, USA.
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Y Kojima,
Y Kojima
Department of Molecular and Experimental Medicine, Scripps Research Institute, La Jolla, CA 92037, USA.
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JS Greengard,
JS Greengard
Department of Molecular and Experimental Medicine, Scripps Research Institute, La Jolla, CA 92037, USA.
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JH Griffin
JH Griffin
Department of Molecular and Experimental Medicine, Scripps Research Institute, La Jolla, CA 92037, USA.
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Blood (1995) 85 (12): 3405–3411.
Citation
MJ Heeb, Y Kojima, JS Greengard, JH Griffin; Activated protein C resistance: molecular mechanisms based on studies using purified Gln506-factor V. Blood 1995; 85 (12): 3405–3411. doi: https://doi.org/10.1182/blood.V85.12.3405.bloodjournal85123405
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