Kar E G, Aune K C
Biochemistry. 1981 Aug 4;20(16):4638-46. doi: 10.1021/bi00519a019.
The behavior of Escherichia coli 50S ribosomal subunit proteins L7/L12 has been investigated in ribosome reconstitution buffer, TMK buffer, by sedimentation equilibrium and analytical gel filtration. Contrary to previous reports that L7/L12 exists in solution solely as dimer species [Möller, W., Groene, A., Terhorst, C., & Amons, R. (1972) Eur J. Biochem. 25, 5], results presented here indicate that L7/L12 undergoes a monomer-dimer-tetramer self-association, with equal equilibrium constants of 3.5 x 10(4) M-1 obtained for the monomer-dimer and dimer-tetramer steps. These results yield standard Gibbs' free energies of -6.1 +/ 0.6 kcal/mol at 20 degrees C. The observed absence of temperature dependence of this interaction over the range 5-25 degrees C indicated a zero standard enthalpy of self-association. Gel filtration results are presented that confirm the highly elongated shape of the L7/L12 molecule. The data suggest the corresponding Stokes radii for the monomer, dimer, and tetramer are 21-23, 26-28, and 29-32 omicron A, respectively. The significance of these results is discussed.
通过沉降平衡和分析凝胶过滤法，在核糖体重构缓冲液TMK缓冲液中研究了大肠杆菌50S核糖体亚基蛋白L7/L12的行为。与之前报道称L7/L12在溶液中仅以二聚体形式存在[Möller, W., Groene, A., Terhorst, C., & Amons, R. (1972) Eur J. Biochem. 25, 5]相反，此处给出的结果表明L7/L12会经历单体-二聚体-四聚体的自缔合过程，单体-二聚体和二聚体-四聚体步骤的平衡常数均为3.5×10⁴ M⁻¹。在20℃时，这些结果得出的标准吉布斯自由能为-6.1±0.6 kcal/mol。在5-25℃范围内观察到这种相互作用不存在温度依赖性，这表明自缔合的标准焓为零。给出的凝胶过滤结果证实了L7/L12分子的高度细长形状。数据表明单体、二聚体和四聚体相应的斯托克斯半径分别为21-23、26-28和29-32埃。讨论了这些结果的意义。
