Department of Chemistry, Yale University, New Haven, Connecticut.
Biophys J. 2024 Sep 17;123(18):3010-3023. doi: 10.1016/j.bpj.2024.05.032. Epub 2024 Jun 6.
The elongation phase of protein synthesis is a cyclic, steady-state process. It follows that its directionality is determined by the thermodynamics of the accompanying chemical reactions, which strongly favor elongation. Its irreversibility is guaranteed by its coupling to those reactions, rather being a consequence of any of the conformational changes that occur as it unfolds. It also follows that, in general, the rate of elongation is not proportional to the forward rate constants of any of its steps, including its final, mechano-chemical step, translocation. Instead, the reciprocal of the rate of elongation should be linearly related to the reciprocal of those rate constants. When the results of experiments done a decade ago to measure the effect that forces opposing translocation have on the rate of elongation are reinterpreted in light of these findings, it becomes clear that translocation was rate limiting under conditions in which those experiments were done, and that it is likely to be a Brownian ratchet process, as was concluded earlier.
蛋白质合成的延伸阶段是一个循环的稳态过程。因此，它的方向性由伴随的化学反应的热力学决定，这些反应强烈有利于延伸。它的不可逆性是由它与这些反应的耦合保证的，而不是由于其展开过程中发生的任何构象变化的结果。这也意味着，一般来说，延伸的速度与它的任何步骤的正向速率常数不成比例，包括其最后的机械化学步骤，转位。相反，延伸速度的倒数应该与这些速率常数的倒数呈线性关系。当十年前进行的实验结果重新解释，以测量对抗转位的力对延伸速度的影响时，根据这些发现，转位在进行这些实验的条件下是限速的，并且它很可能是一个布朗棘轮过程，正如之前得出的结论。
