Parr G R, Taniuchi H
J Biol Chem. 1983 Mar 25;258(6):3759-63.
A noncovalently bound, ordered complex consisting of fragments (1-25)H and (14-103) derived from tuna cytochrome c has been prepared and characterized. The equilibrium properties of this complex are indistinguishable from those of the corresponding complex, (1-25)H X (23-104), of horse cytochrome c. The tuna species possesses a second tryptophan residue (at position 33 of the amino acid sequence and replacing the histidine residue of the horse protein) whose fluorescence is also essentially fully quenched in the native form and in the complex. It is found that for the tuna complex, the fluorescence of both tryptophans is fully quenched during the second order phase of the reaction mechanism. This provides evidence for the compact nature of the intermediate complexes formed at this stage of the complementation process (Parr, G. R., and Taniuchi, H. (1982) J. Biol. Chem. 257, 10103-10111). The observed second order rate constant for the tuna fragments is reduced by a factor of two from that for the horse fragments. During the first order kinetic phase corresponding to the transition from the intermediate complexes to the native complex, qualitative as well as quantitative differences are also observed between the tuna and the horse species. The kinetics of complementation of the "hybrid" complexes is also reported. This exchangeability of both the heme fragment and the apofragment of the complex between these two species indicates close similarity of the folding mechanism. Nonetheless, the results also serve to highlight the subtle effects exerted on the folding process by a relatively small number of changes (17%) in the amino acid sequence.
一种由金枪鱼细胞色素c衍生的片段(1 - 25)H和(14 - 103)组成的非共价结合的有序复合物已被制备并表征。该复合物的平衡性质与马细胞色素c相应复合物(1 - 25)H X (23 - 104)的平衡性质无法区分。金枪鱼物种有第二个色氨酸残基（在氨基酸序列的第33位，取代了马蛋白的组氨酸残基），其荧光在天然形式和复合物中也基本完全淬灭。研究发现，对于金枪鱼复合物，在反应机制的二级阶段，两个色氨酸的荧光都完全淬灭。这为在互补过程的这个阶段形成的中间复合物的紧密性质提供了证据(帕尔，G. R.，和谷内，H. (1982) J.生物化学杂志257, 10103 - 10111)。观察到的金枪鱼片段的二级速率常数比马片段的二级速率常数降低了两倍。在对应于从中间复合物向天然复合物转变的一级动力学阶段，金枪鱼和马物种之间也观察到了定性和定量的差异。还报道了“杂交”复合物的互补动力学。复合物的血红素片段和脱辅基片段在这两个物种之间的这种可交换性表明折叠机制非常相似。尽管如此，结果也凸显了氨基酸序列中相对少量的变化(17%)对折叠过程产生的微妙影响。
