肝素抗Xa因子特性的相对分子质量依赖性
The relative molecular mass dependence of the anti-factor Xa properties of heparin.
作者信息
Ellis V, Scully M F, Kakkar V V
出版信息
Biochem J. 1986 Sep 1;238(2):329-33. doi: 10.1042/bj2380329.
The effect of heparin fractions of various Mr, with high affinity for antithrombin III, on the kinetics of the reaction between factor Xa and antithrombin III have been studied using purified human proteins. Each of the heparin fractions, which varied between pentasaccharide and Mr 32,000, accelerated the inhibition of factor Xa although an increasing rate of inhibition was observed with increasing Mr. The chemically synthesized pentasaccharide preparation (Mr 1714) gave a maximum inhibition rate constant of 1.2 X 10(7) M-1 X min-1, compared with 6.3 X 10(4) M-1 X min-1 in the absence of heparin, and this rose progressively to 4.2 X 10(8) M-1 X min-1 with the two fractions of highest Mr (22,500 and 32,000). The 35-fold difference in inhibition rates observed with the high-affinity fractions was virtually abolished by the presence of 0.3 M-NaCl. The disparity in these rates of inhibition was shown to be due to a change in the Km for factor Xa when a two-substrate model of heparin catalysis was used. The Km for factor Xa rose from 28 nM for the fraction of Mr 32,000 to 770 nM for the pentasaccharide, whilst 0.3 M-NaCl also caused an increase in Km with the high-Mr fraction. These data suggest that the increased rates of inhibition observed with heparins of higher Mr may be due to an involvement of heparin binding to factor Xa as well as to antithrombin III.
利用纯化的人源蛋白质，研究了对抗凝血酶III具有高亲和力的不同相对分子质量（Mr）的肝素片段对Xa因子与抗凝血酶III之间反应动力学的影响。每一种肝素片段，相对分子质量在五糖至32,000之间变化，均加速了Xa因子的抑制作用，尽管随着相对分子质量的增加，抑制速率也在增加。化学合成的五糖制剂（相对分子质量1714）的最大抑制速率常数为1.2×10⁷ M⁻¹×min⁻¹，而在无肝素时为6.3×10⁴ M⁻¹×min⁻¹，并且随着相对分子质量最高的两个片段（22,500和32,000），该值逐渐升至4.2×10⁸ M⁻¹×min⁻¹。0.3 M氯化钠的存在几乎消除了高亲和力片段观察到的35倍的抑制率差异。当使用肝素催化的双底物模型时，这些抑制率的差异表明是由于Xa因子的米氏常数（Km）发生了变化。Xa因子的Km从相对分子质量为32,000的片段的28 nM升至五糖的770 nM，同时0.3 M氯化钠也导致高相对分子质量片段的Km增加。这些数据表明，相对分子质量较高的肝素观察到的抑制率增加可能是由于肝素与Xa因子以及抗凝血酶III结合所致。
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