Proteolytic Interactions of Factor IXa With Human Factor VIII and Factor VIIIa

Factor IXa was shown to inactivate both factor VIII and factor VIIIa in a phospholipid-dependent reaction that could be blocked by an antifactor IX antibody. Factor IXa-catalyzed inactivation correlated with proteolytic cleavages within the A1 subunit of factor VIIIa and within the heavy chain (cont...

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Bibliographic Details
Published in:Blood 1992-12, Vol.80 (12), p.3120-3126
Main Authors: Lamphear, Barry J., Fay, Philip J.
Format: Article
Language:English
Subjects:
Amino Acid Sequence
Biological and medical sciences
Blood coagulation. Blood cells
Blotting, Western
Coagulation factors
Endopeptidases - metabolism
Factor IXa - metabolism
Factor VIII - metabolism
Factor VIIIa - metabolism
Fundamental and applied biological sciences. Psychology
Humans
Kinetics
Molecular and cellular biology
Molecular Sequence Data
Peptide Fragments - isolation & purification
Phospholipids - pharmacology
Time Factors
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Summary:Factor IXa was shown to inactivate both factor VIII and factor VIIIa in a phospholipid-dependent reaction that could be blocked by an antifactor IX antibody. Factor IXa-catalyzed inactivation correlated with proteolytic cleavages within the A1 subunit of factor VIIIa and within the heavy chain (contiguous A1-A2-B domains) of factor VIII. Furthermore, a relatively slow conversion of factor VIII light chain to a 68-Kd fragment was observed after prolonged incubation. Sites of cleavage were identified within the AI domain at Arg336-Met337 and within the factor VIII light chain at Arg1719-Asn1720. Factor IXa failed to cleave isolated factor VIII heavy chains, yet cleaved isolated factor VIII light chain. In addition, the purified A1/A3-C1-C2 dimer derived from factor VIIIa was a substrate for factor IXa; however, cleavage of the A1 subunit occurred at less than 30% the rate of cleavage of A1 in trimeric factor VIIIa. These data suggest that factor VIII light chain contributes to the binding site for factor IXa and also support a role for a heavy chain determinant located within the A2 subunit in the association of factor VIIIa with factor IXa. Furthermore, the capacity of factor IXa to proteolytically inactivate its cofactor, factor VIIIa, suggests a mode of regulation within the intrinsic tenase complex. © 1992 by The American Society of Hematology.
ISSN:0006-4971
1528-0020
DOI:10.1182/blood.V80.12.3120.3120