A method for identifying cysteine-containing peptides in proteins is presented using 2-bromoacetamido-4-nitrophenol (BNP) to introduce an easily detectable probe. The formation of a covalent bond between the protein sulfhydryl group and the acetamido moiety of BNP introduces a chromophore with an absorbance maximum at 410 nm. The modified protein can then be cleaved with appropriate proteases and the resulting peptides separated by chromatographic methods. Monitoring the effluent at a single wavelength (405 nm) provides a rapid and simple method of detecting and isolating only those peptides which contain cysteine residue(s). The nitrophenol derivative is stable under conditions required for protease cleavage. The reagent is therefore useful for locating cysteine-containing peptides in protein digests and can be used to explore the accessibility of different cysteines under a variety of conditions. The ease of modification, specificity of reaction, product stability, and simple detection of modified peptides make BNP ideal for investigation of cysteine residues.

中文翻译：

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通过2-溴乙酰氨基-4-硝基苯酚修饰修饰的蛋白质巯基的定位和分析。

介绍了一种使用2-溴乙酰氨基-4-硝基苯酚（BNP）引入易于检测的探针鉴定蛋白质中含半胱氨酸的肽的方法。在蛋白质巯基和BNP的乙酰氨基部分之间形成共价键会引入发色团，该发色团在410 nm处具有最大吸光度。然后可以用适当的蛋白酶切割修饰的蛋白质，并通过色谱法分离所得的肽。在单个波长（405 nm）处监测流出物提供了一种快速，简单的方法，可以仅检测和分离含有半胱氨酸残基的那些肽。硝基酚衍生物在蛋白酶切割所需的条件下是稳定的。因此，该试剂可用于在蛋白质消化物中定位含半胱氨酸的肽，并可用于探索在各种条件下不同半胱氨酸的可及性。修饰的简便性，反应的特异性，产物的稳定性以及修饰肽的简单检测使BNP成为研究半胱氨酸残基的理想选择。