蛋白质变性Denaturation (biochemistry)

加热、紫外线、强酸强碱、重金属离子（Hg²⁺、Pb²⁺、Ag⁺）、尿素和盐酸胍、有机溶剂（乙醇）、去污剂（十二烷基硫酸钠）以及剧烈搅拌都能引起变性。它们破坏维持高级结构的氢键、疏水作用、盐桥或二硫键。变性的蛋白质疏水基团暴露，溶解度下降、易聚集沉淀，黏度增加，更容易被蛋白酶水解。

Heat, ultraviolet light, strong acids and bases, heavy-metal ions (Hg²⁺, Pb²⁺, Ag⁺), urea and guanidinium chloride, organic solvents such as ethanol, detergents such as sodium dodecyl sulfate and vigorous agitation all denature proteins by disrupting the hydrogen bonds, hydrophobic interactions, salt bridges or disulfide bonds that hold their structure. Denatured proteins expose hydrophobic groups, become less soluble and aggregate, grow more viscous and are more easily digested by proteases.

1931 年吴宪首次系统提出蛋白质变性学说，认为变性是天然蛋白质紧密有序结构变为松散无序结构的过程。1961 年安芬森用 8 mol/L 尿素和巯基乙醇使核糖核酸酶完全变性并还原二硫键，透析除去试剂后，蛋白质自发复性，恢复约 95% 的活性，证明变性在一定条件下可逆，并说明一级结构包含折叠所需的全部信息。

In 1931 the Chinese biochemist Hsien Wu set out the first systematic theory of denaturation, describing it as the change from a compact, ordered native structure to a loose, disordered one. In 1961 Anfinsen fully denatured ribonuclease with 8 mol/L urea and mercaptoethanol, reducing its disulfide bonds; after the reagents were removed by dialysis it refolded spontaneously and recovered about 95% of its activity, showing that denaturation can be reversible and that the sequence holds all the information needed to fold.

煮鸡蛋时蛋清变白凝固、牛奶加酸凝成奶酪、用 75% 乙醇和高温高压灭菌、豆浆加卤水做豆腐，都与蛋白质变性或沉淀有关。重金属中毒时可服用大量牛奶或蛋清进行急救。实验室用 SDS 使蛋白质变性后进行聚丙烯酰胺凝胶电泳，按分子量分离。

Egg white turning white and solid on boiling, milk curdling with acid for cheese, sterilising with 75% ethanol or autoclaving, and making tofu by adding brine to soy milk all involve protein denaturation or precipitation. In heavy-metal poisoning large amounts of milk or egg white can be given as first aid. In the laboratory, SDS denatures proteins for polyacrylamide gel electrophoresis, which separates them by mass.