蛋白质Protein

一级结构是氨基酸序列；二级结构是主链通过氢键形成的 α 螺旋、β 折叠等局部构象；三级结构是整条链在疏水作用、氢键、离子键和二硫键作用下折叠成的三维结构；四级结构是多个亚基的组装方式。1961 年安芬森的核糖核酸酶实验表明，一级序列决定三维结构。2020 年 AlphaFold 实现了接近实验精度的结构预测，2024 年诺贝尔化学奖授予蛋白质设计与结构预测。

Primary structure is the amino-acid sequence; secondary structure is local backbone conformation such as α-helices and β-sheets held by hydrogen bonds; tertiary structure is the whole chain's three-dimensional fold, shaped by hydrophobic interactions, hydrogen bonds, ionic bonds and disulfide bridges; quaternary structure is how subunits assemble. Anfinsen's ribonuclease experiments in 1961 showed that sequence determines structure. AlphaFold reached near-experimental accuracy in structure prediction in 2020, and the 2024 Nobel Prize in Chemistry honoured protein design and structure prediction.

1838 年穆尔德在贝采利乌斯建议下用 protein（希腊语“首要的”）命名这类物质。1902 年费歇尔和霍夫迈斯特提出蛋白质由氨基酸以肽键连接。1951 年鲍林提出 α 螺旋和 β 折叠模型。1955 年桑格测定胰岛素序列。1958 年肯德鲁解析出肌红蛋白的三维结构，这是第一个被解析的蛋白质结构。

In 1838 Mulder, on Berzelius's suggestion, named these substances protein, from the Greek for 'primary'. In 1902 Fischer and Hofmeister proposed that proteins are amino acids joined by peptide bonds. Pauling proposed the α-helix and β-sheet in 1951, Sanger sequenced insulin in 1955, and in 1958 Kendrew solved the three-dimensional structure of myoglobin, the first protein structure determined.

蛋白质有两性和等电点；受热、强酸强碱、重金属盐、有机溶剂和紫外线作用会变性；与双缩脲试剂呈紫色，含芳香氨基酸的蛋白质与浓硝酸呈黄色（黄蛋白反应）。人体不能合成 9 种必需氨基酸，需从食物中获取。成人每日蛋白质推荐摄入量约为 0.8 g/kg 体重。

Proteins are amphoteric with an isoelectric point and are denatured by heat, strong acids and bases, heavy-metal salts, organic solvents and UV light. They give a violet colour with the biuret reagent, and proteins with aromatic amino acids turn yellow with concentrated nitric acid (the xanthoproteic reaction). Humans cannot make nine essential amino acids and must eat them; the adult recommended intake is about 0.8 g of protein per kg of body weight a day.