Gitlin Irina, Gudiksen Katherine L, Whitesides George M
Department of Chemistry and Chemical Biology, Harvard University, 12 Oxford Street, Cambridge, Massachusetts 02138, USA.
J Phys Chem B. 2006 Feb 9;110(5):2372-7. doi: 10.1021/jp055699f.
Bovine carbonic anhydrase (BCA) and its derivative with all lysine groups acetylated (BCA-Ac18) have different stabilities toward denaturation by sodium dodecyl sulfate (SDS). This difference is kinetic: BCA-Ac18 denatures more slowly than BCA by several orders of magnitude over concentrations of SDS ranging from 2.5 to 10 mM. The rates of renaturation of BCA-Ac18 are greater than those of BCA, when these proteins are allowed to refold from a denatured state ([SDS]=10 mM) to a folded state ([SDS]=0.1 to 1.5 mM). On renaturation, the yields of the correctly folded protein (either BCA or BCA-Ac18) decrease with increasing concentration of SDS. At intermediate concentrations of SDS (from 0.7 to 2 mM for BCA, and from 1.5 to 2 mM for BCA-Ac18), both unfolding and refolding of the proteins are too slow to be observed; an alternative process-probably aggregation-competes with refolding of the denatured proteins at those intermediate concentrations. Because it is experimentally impractical to prove equilibrium, it is not possible to establish whether there is a difference in the thermodynamics of unfolding/refolding between BCA and BCA-Ac18.
牛碳酸酐酶(BCA)及其所有赖氨酸基团均被乙酰化的衍生物(BCA-Ac18)对十二烷基硫酸钠(SDS)变性的稳定性不同。这种差异是动力学上的:在2.5至10 mM的SDS浓度范围内,BCA-Ac18的变性速度比BCA慢几个数量级。当这些蛋白质从变性状态([SDS]=10 mM)复性到折叠状态([SDS]=0.1至1.5 mM)时,BCA-Ac18的复性速率大于BCA。复性时,正确折叠的蛋白质(BCA或BCA-Ac18)的产量随SDS浓度的增加而降低。在中等浓度的SDS下(BCA为0.7至2 mM,BCA-Ac18为1.5至2 mM),蛋白质的解折叠和复折叠都太慢而无法观察到;在这些中等浓度下,一个替代过程——可能是聚集——与变性蛋白质的复折叠竞争。由于通过实验证明平衡不切实际,因此无法确定BCA和BCA-Ac18在解折叠/复折叠热力学上是否存在差异。