Farwell M A, Schirawski J, Hager P W, Spremulli L L
Department of Biology, East Carolina University, Greenville, NC 27858, USA.
Biochim Biophys Acta. 1996 Nov 11;1309(1-2):122-30. doi: 10.1016/s0167-4781(96)00118-2.
The small subunit of the bovine mitochondrial ribosome forms a tight complex with mRNAs. This [28 S:mRNA] complex forms as readily on circular mRNAs as on linear mRNAs indicating that a free 5' end on the mRNA is not required for the interaction observed. The effects of monovalent cations on the equilibrium association constant and on the forward and reverse rate constants governing this interaction have been determined. Monovalent cations have a strong effect on the forward rate constant. Increasing the KCl concentration from 1 mM to 100 mM reduces kon by nearly 100-fold. Monovalent cations have only a small effect on the reverse rate constant, koff'. Analysis of these data indicates that the rate laws governing the formation and dissociation of the [28 S:mRNA] complex cannot be deduced from the chemical equation. This observation suggests that there are "hidden intermediates' in the formation and dissociation of this complex. The implications of these observations are discussed in terms of a model for the interaction between the mitochondrial 28 S subunit and mRNAs.
牛线粒体核糖体的小亚基与信使核糖核酸（mRNA）形成紧密复合物。这种[28 S:mRNA]复合物在环状mRNA上形成的速度与在线性mRNA上形成的速度一样快，这表明mRNA上的游离5'端对于所观察到的相互作用并非必需。已确定单价阳离子对平衡缔合常数以及控制这种相互作用的正向和反向速率常数的影响。单价阳离子对正向速率常数有很强的影响。将氯化钾（KCl）浓度从1毫摩尔/升增加到100毫摩尔/升会使正向速率常数（kon）降低近100倍。单价阳离子对反向速率常数（koff'）只有很小的影响。对这些数据的分析表明，控制[28 S:mRNA]复合物形成和解离的速率定律无法从化学方程式推导出来。这一观察结果表明，在该复合物的形成和解离过程中存在“隐藏中间体”。根据线粒体28 S亚基与mRNA之间相互作用的模型对这些观察结果的意义进行了讨论。
