Formation of factors IXa and Xa by the extrinsic pathway - Differential regulation by tissue factor pathway inhibitor and antithrombin III
Formation of factors IXa and Xa by the extrinsic pathway - Differential regulation by tissue factor pathway inhibitor and antithrombin III
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DOI：
10.1074/jbc.m312827200
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发表时间：
2004-04-23
影响因子：
4.8
通讯作者：
Krishnaswamy, S
中科院分区：
文献类型：
--
作者：
Lu, G;Broze, GJ;Krishnaswamy, S
通过VIIa/TF激活因子X和通过组织因子途径抑制剂（TFPI）对酶复合物的Xa依赖性抑制被认为是凝血起始的主要步骤。通过VIIa/TF的IX活化被认为有助于在随后的扩增阶段中进一步产生Xa所需的催化剂。我们已经调查了Xa和IXabeta生产VIIa-TF在一个系统中重建与X和IX和主要的生理抑制剂，这一途径TFPI和抗凝血酶III（AT）。无抑制剂的动力学研究表明，IX和X作为VIIa/TF的竞争性替代底物，具有相似的动力学常数。当IX和X都存在时，TFPI显著抑制IXabeta或Xa的形成程度。相反，AT迅速耗尽活性Xa，对IXabeta形成的影响很小。当AT和TFPI都存在时，无论VIIa/TF浓度如何，活性IXabeta的形成均显著超过活性Xa的形成。这些发现可以通过包含单个激活和抑制步骤的动力学的模型来定量解释。通过该途径的活性Xa形成主要通过其被AT快速失活来调节。相反，TFPI的Xa依赖性抑制反应在限制酶原消耗和活性IXabeta的形成中起主要作用。这些调节现象产生活性IXabeta作为VIIa/TF的主要而非次要产物。我们的研究结果提出了一种可能性，IXabeta产生的外源性途径，其功能内的内在Xase复合物激活X的能力可能发挥重要作用，在生产Xa必要的启动和持续阶段的促凝血反应血管损伤后。
The activation of factor X by VIIa/TF and the Xa-dependent inhibition of the enzyme complex by tissue factor pathway inhibitor ( TFPI) are considered primary steps in the initiation of coagulation. IX activation by VIIa/TF is considered to contribute catalyst necessary for further Xa production in the ensuing amplification phase. We have investigated Xa and IXabeta production by VIIa-TF in a system reconstituted with both X and IX and the principal physiologic inhibitors of this pathway TFPI and antithrombin III (AT). Kinetic studies without inhibitors established that IX and X functioned as competitive alternate substrates for VIIa/TF with similar kinetic constants. When both IX and X were present, TFPI significantly inhibited the extent of formation of either IXabeta or Xa. In contrast, AT rapidly depleted active Xa with a small effect on IXabeta formation. When both AT and TFPI were present, active IXabeta formation significantly exceeded the formation of active Xa regardless of the VIIa/TF concentration. These findings could be quantitatively accounted for by a model encompassing the kinetics of the individual activation and inhibition steps. Active Xa formation by this pathway is regulated in a principal way by its rapid inactivation by AT. In contrast, the Xa-dependent inhibitory reactions of TFPI play a primary role in limiting zymogen consumption and the formation of active IXabeta. These regulatory phenomena yield active IXabeta as a major rather than secondary product of VIIa/TF. Our findings raise the possibility that IXabeta produced by the extrinsic pathway, and its ability to function within the intrinsic Xase complex to activate X may play a significant role in producing Xa necessary for both the initiation and sustained phases of the procoagulant response following vascular damage.