每周分子Molecule of the Week
Molecule of the Week: L-Alanine and L-Serine
每周分子：L-丙氨酸和L-丝氨酸
L-丙氨酸1和L-丝氨酸1是蛋白质生物合成所必需的氨基酸。因为人体内能够合成这两种氨基酸，所以它们被认为不是人类（及其它大多动物）饮食中的必需品。
1850年，德国化学家Adolph Strecker从乙醛中合成了丙氨酸，之后很久丙氨酸才被从天然物质中发现并分离出来。当然，Strecker制备的是D, L-型氨基酸外消旋体，而不是任何一个单独的异构体。
另一方面，德国化学家Emil Cramer于1865年在自然界中首次发现了丝氨酸，特别是在丝蛋白中。而且，说到丝……
丙氨酸和丝氨酸，以及之前每周分子的甘氨酸和L-脯氨酸，是蜘蛛丝蛋白中的主要氨基酸。富含丙氨酸的晶体区域提供了丝强度，而富含甘氨酸的非晶区域则提供了弹性。
万圣节让我们想起蜘蛛。蜘蛛编制丝网。丝是由蛋白质组成的。蛋白质是氨基酸的聚合物。谁能想到这么简单的分子会让人害怕呢?
1所有通过生物合成为蛋白质的氨基酸都是L-对映异构体。一些D-对映异构体也出现在自然界中，但相对少见。
L-丙氨酸信息速览
| CAS登记号 | 56-41-7 |
| 分子式 | C3H7NO2 |
| 摩尔质量 | 89.09 g/mol |
| 外观 | 白色晶体或粉末 |
| 熔点 | ≈300 ºC (分解) |
| 水溶性 | 167 g/L |
L-丝氨酸信息速览
| CAS 登记号 | 56-45-1 |
| 分子式 | C3H7NO3 |
| 摩尔质量 | 105.09 g/mol |
| 外观 | 白色晶体或粉末 |
| 熔点 | 220–250 ºC (分解) |
| 水溶性 | 425 g/L |
L-丙氨酸危害信息
| GHS 分类*: 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-Alanine1 and L-serine1 are amino acids that are necessary for the biosynthesis of proteins. They are considered “nonessential” in human diets (and those of most other animals) because they are synthesized in the body.
In 1850, long before it was discovered in and isolated from natural substances, alanine was synthesized from acetaldehyde by German chemist Adolph Strecker. Of course, Strecker made the D,L-racemate of the amino acid rather than either isomer alone.
Serine, on the other hand, was first discovered in nature, specifically in silk protein, by German chemist Emil Cramer in 1865. And, speaking of silk . . .
Alanine and serine, along with previous Molecules of the Week glycine and L-proline, are the major amino acids in spider silk proteins. Alanine-rich crystalline areas give silk strength, whereas glycine-rich amorphous regions provide elasticity.
Halloween reminds us of spiders. Spiders spin webs of silk. Silk is made up of proteins. Proteins are polymers of amino acids. Who would have thought that such simple molecules could be scary?
1All amino acids that are biosynthesized into proteins are the L-enantiomers. Some D-enantiomers appear in nature, but they are relatively rare.
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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