Woodward C K, Ellis L M, Rosenberg A
J Biol Chem. 1975 Jan 25;250(2):440-4.
The effects of ethanol, ethylene glycol, dioxane, and other organic co-solvents upon the hydrogen exchange rates of randomly coiled oxidized RNase, native RNase, and native trypsin have been measured. The exchange rate of oxidized RNase, the model compound for the proton transfer step in hydrogen exchange, is decreased by all of the co-solvents studied at temperatures in the range 3-20 degrees. This has been ascribed to the combined effects of the disruption of peptide bond solvation due to a reduction in the concentration of water, and of changes in [OH-] ion concentration due to changes in the acid dissociation constant of water, Kw. The solvent dependence for both native RNase and native trypsin is similar in all of the solvents studied. At a low temperature (3-20 degrees), the exchange rates go through a minimum as the solvent concentration is increased. At higher temperatures (20-35 degrees) the exchange rates are increased at all concentrations of the co-solvent. The apparent rate minimum at lower temperatures is due to two opposing effects. Co-solvents decrease the rate of exchange that occurs directly from the folded molecule. At higher concentrations and higer temperature. The decrease in rates for exchange directly from folded protein is primarily due to the effects on the proton transfer step, and not to binding or the solvent effects on protein structure. The solvents used in this study have no apparent effect on conformational processes contributing to the hydrogen exchange process in folded proteins.
已测定乙醇、乙二醇、二氧六环及其他有机共溶剂对无规卷曲氧化核糖核酸酶、天然核糖核酸酶和天然胰蛋白酶氢交换速率的影响。在3至20摄氏度范围内，所有研究的共溶剂均会降低氧化核糖核酸酶（氢交换中质子转移步骤的模型化合物）的交换速率。这归因于水浓度降低导致肽键溶剂化破坏以及水的酸解离常数Kw变化引起的[OH-]离子浓度变化的综合影响。在所有研究的溶剂中，天然核糖核酸酶和天然胰蛋白酶对溶剂的依赖性相似。在低温（3至20摄氏度）下，随着溶剂浓度增加，交换速率先经历一个最小值。在较高温度（20至35摄氏度）下，共溶剂在所有浓度下都会使交换速率增加。较低温度下明显的速率最小值是由两种相反的效应导致的。共溶剂降低了直接从折叠分子发生的交换速率。在较高浓度和较高温度下，直接从折叠蛋白发生的交换速率降低主要是由于对质子转移步骤的影响，而非对蛋白质结构的结合或溶剂效应。本研究中使用的溶剂对折叠蛋白中氢交换过程的构象过程没有明显影响。
