Chaires J B, Kegeles G, Wahba A J
Biophys Chem. 1979 May;9(4):405-12.
Addition of initiation factor IF3 to solutions of E. coli ribosomes dramatically alters their behavior in pressure-jump relaxation kinetic experiments in which 90 degrees light-scattering is used to monitor the macromolecular reaction. The effect of IF3 on relaxation processes attributed to "tight" couples is strongly dependent on the Mg2+ concentration. At 2.5 mM Mg2+, addition of 1 molar equivalent of IF3 decreases the relaxation amplitude by a factor of 3 relative to ribosome solutions without IF3. However, at 5.0 mM Mg2+, addition of 1 molar equivalent of IF3 produces a marked increase in the relaxation amplitude, by a factor of 2-8 fold relative to ribosomes in the absence of IF3. IF3 has no effect on the relaxation process attributed to "loose" couples at 10 mM Mg2+. While we are unable to propose a precise mechanism for IF3 action with the data on hand, our results require that the 30S . IF3 complex either reacts with the 50S subunit, forming a 70S . IF3 intermediate, or acts as a pool of reactive 30S subunit. Further kinetic evidence is required to distinguish between these possible pathways.
向大肠杆菌核糖体溶液中添加起始因子IF3，会显著改变其在压力跳跃弛豫动力学实验中的行为，该实验中使用90度光散射来监测大分子反应。IF3对归因于“紧密”偶联的弛豫过程的影响强烈依赖于Mg2+浓度。在2.5 mM Mg2+时，添加1摩尔当量的IF3会使弛豫幅度相对于不含IF3的核糖体溶液降低3倍。然而，在5.0 mM Mg2+时，添加1摩尔当量的IF3会使弛豫幅度显著增加，相对于不存在IF3时的核糖体增加2 - 8倍。在10 mM Mg2+时，IF3对归因于“松散”偶联的弛豫过程没有影响。虽然我们无法根据手头的数据提出IF3作用的精确机制，但我们的结果表明30S.IF3复合物要么与50S亚基反应，形成70S.IF3中间体，要么作为反应性30S亚基的一个库。需要进一步的动力学证据来区分这些可能的途径。
