每周分子Molecule of the Week
Molecule of the Week: L-Cysteine
每周分子：L-半胱氨酸
L-半胱氨酸是含有硫原子的两种蛋白氨基酸中的一种(另一种是蛋氨酸)。因为L-半胱氨酸是在人体内生成的，所以被认为是一种非必需氨基酸。但是，对于缺乏半胱氨酸的人而言，却需要服用补充剂进行治疗。
半胱氨酸被氧化时，两个硫醇中的氢原子被消除，硫原子结合形成L-胱氨酸的二聚体。在生物体中，单体与二聚体很容易互换；因此，这两种酸在营养上是相似的。
2018年9月，哈佛大学医学院的David Corey和波士顿儿童医院的Jeffrey Hold报告说，半胱氨酸在改善人类听力方面可能发挥作用。他们发现内耳毛细胞中的TMC1蛋白会形成毛孔，这些毛孔负责将声音转换成电信号传递给大脑。在一些个体中，TMC1突变可能导致耳聋。
研究人员用半胱氨酸取代TMC1中的残基，然后用体积大的带电基团修饰半胱氨酸基团。这种人为的突变导致蛋白质停止产生电流，从而验证了突变的TMC1抑制了听力。
这些发现表明，以TMC1突变为靶点的药物或替代突变蛋白的基因疗法可以帮助受TMC1突变影响的个体恢复听力。
L-半胱氨酸信息速览
| CAS 登记号 | 52-90-4 |
| 分子式 | C3H7NO2S |
| 摩尔质量 | 121.16 |
| 外观 | 白色晶体或粉末 |
| 熔点 | 240 ºC (分解) |
| 水溶性 | ≈280 g/L |
L-半胱氨酸危害信息
| GHS 分类信息*:非危害物质或混合物 |
【关于每周分子 】
自2001年以来，“每周分子”已成为广受欢迎的栏目。多数分子由读者推荐。每个结构都经由科学家审查，并以3-D和平面图像的形式显示，同时附有该分子简介。可以通过美国化学文摘社（CAS）提供的SciFinder中的CAS REGISTRY获取每周分子的更多信息。CAS REGISTRY中的每条物质信息都展示了物质的CAS登记号、索引名、通用名、商品名、书目信息等其他更多信息。发送邮件至motw@acs.org推荐您感兴趣的分子。
L-Cysteine is one of the two proteinogenic amino acids that contain a sulfur atom (the other is methionine). It is considered a nonessential amino acid because it is produced in the human body. Individuals who are deficient in cysteine, however, must be treated with supplements.
When cysteine is oxidized, the two thiol hydrogen atoms are eliminated, and the sulfur atoms join to form the dimer L-cystine. In biological systems, the monomer and dimer interchange easily; thus, both acids are nutritionally similar.
In September 2018, David Corey at Harvard Medical School and Jeffrey Hold of Boston Children’s Hospital reported that cysteine could play a role in improving hearing in humans. They discovered that the TMC1 protein in the inner ear’s hair cells forms pores that are involved in converting sound to electrical signals to the brain. In some individuals, a mutation in TMC1 can lead to deafness.
The researchers substituted residues in TMC1 with cysteine and then modified the cysteine groups with bulky charged groups. This artificial mutation caused the protein to cease the production of electric current, thus verifying that mutated TMC1 inhibits hearing.
These findings suggest that drugs that target TMC1 mutations or gene therapies that replace the mutated protein could help restore hearing to affected individuals.
L-Cysteine fast facts fast facts
| CAS Reg. No. | 52-90-4 |
| Empirical formula | C3H7NO2S |
| Molar mass | 121.16 |
| Appearance | White crystals or powder |
| Melting point | 240 ºC (dec.) |
| Water solubility | ≈280 g/L |
L-Cysteine hazard information
| GHS classification*: not a hazardous substance or mixture |
*Globally Harmonized System of Classification and Labeling of Chemicals. Explanation of pictograms.
About Molecule of the Week
MOTW has been a popular feature on ACS website since 2001. Many molecules are suggested by our website visitors. Every structure is reviewed by a scientist and displayed in 3-D and flat images with a brief description. Each week’s molecule also links to a sample record from the CAS REGISTRY, which is searched using SciFinder. Each record displays the registry number, index name and synonyms, bibliographic information, and more. Send us a molecule suggestion at motw@acs.org.
Copyright © 2018 American Chemical Society.
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