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			PubMed Journals: J Biol Chem

  Source:		PMID: 2040636


    		J Biol Chem. 1991 Jun 15;266(17):11317-27.
     
			Cooperative activation of human factor IX
			by the human extrinsic pathway of blood
			coagulation.

			Lawson JH(1), Mann KG.

			Author Information
			(1) Department of Biochemistry,
			University of Vermont, Burlington 05405.

			The activation of human coagulation factor IX
			by human tissue factor.factor VIIa.PCPS.Ca2+
			(TF.VIIa.PCPS.Ca2+) and factor Xa.PCPS.Ca2+
			enzyme complexes was investigated. Reactions
			were performed in a highly purified system
			consisting of isolated human plasma proteins
			and recombinant human tissue factor with
			synthetic phospholipid vesicles (PCPS: 75%
			phosphatidylcholine (PC), 25% phosphatidylserine
			(PS)). Factor IX activation was evaluated
			by sodium dodecyl sulfate-polyacrylamide
			gel electrophoresis, [3H]factor IX activation
			peptide assay, colorimetric substrate thiobenzyl
			benzyloxycarbonyl-L-lysinate (Z-Lys-SBzl)
			hydrolysis, and specific incorporation of
			a fluorescent peptidyl chloromethyl ketone.
			Factor IX activation by the TF.VIIa.PCPS.Ca2+
			enzyme complex was observed to proceed through
			the obligate non-enzymatic intermediate
			species factor IX alpha. The simultaneous
			activation of human coagulation factors
			IX and X by the TF.VIIa.PCPS.Ca2+ enzyme
			complex were investigated. When factors
			IX and X were presented to the TF.VIIa complex,
			at equal concentrations, it was observed
			that the rate of factor IX activation remained
			unchanged while the rate of factor X activation
			slowed by 45%. When the proteolytic cleavage
			products of this reaction were analyzed
			by sodium dodecyl sulfate-polyacrylamide
			gel electrophoresis, it was observed that
			the intermediate species factor IX alpha
			was generated more rapidly when factor X
			was present in the reaction mixture. When
			factor IX was treated with factor Xa.PCPS
			in the presence of Ca2+, it was observed
			that factor IX was rapidly converted to
			factor IX alpha. The activation of factor
			IX alpha by the TF.VIIa.PCPS.Ca2+ complex
			was evaluated, and it was observed that
			factor IX alpha was activated more rapidly
			by the TF.VIIa.PCPS.Ca2+ complex than was
			factor IX itself. These data suggest that
			factors IX and X, when presented to the
			TF.VIIa.PCPS.Ca2+ enzyme complex, are both
			rapidly activated and that factor Xa, which
			is generated in the initial stages of the
			extrinsic pathway, participates in the first
			proteolytic step in the activation of factor
			IX, the generation of factor IX alpha.

			PMID: 2040636 [Indexed for MEDLINE]

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