What molecules are we?
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.
L-Alanine hazard information
| GHS classification*: not a hazardous substance or mixture |
*Globally Harmonized System of Classification and Labeling of Chemicals. Explanation of pictograms.
L-Serine hazard information
| GHS classification: not a hazardous substance or mixture |
MOTW update: March 16, 2026
L-Alanine1 is a “nonessential” amino acid because it is made by the body; but it is necessary for the biosynthesis of proteins.
Last month, Mika Yoshioka*, Hiroki Kobayashi, and Hiroyuki Kagi* at the University of Tokyo reported the discovery of a mechanism that nature might have used to maximize homochirality in amino acids. Positing that early in Earth’s history there was only a small enantiomeric excess of L-alanine, they examined a potential physicochemical mechanism for enhancing the L-enantiomer via the pressure-induced dissolution and crystallization behavior of it and its racemate (DL-alanine2) in aqueous solution.
The geochemists compressed a single crystal of each form of alanine in saturated aqueous solution to ≈0.8 GPa and measured the solubilities of the L-enantiomer and the racemate. The solubility of L-alanine increased significantly, whereas the racemate’s solubility was almost unchanged. Most of the racemate remained in crystal form, entrapped in the high-pressure ice layer. The result was enrichment of bioavailable L-alanine. The authors observed that this selective crystallization could have existed in Earth’s early oceans.
1. CAS Reg. No. 56-41-7.
2. CAS Reg. No. 302-72-7.
L-Alanine fast facts
| CAS Reg. No. | 56-41-7 |
| Empirical formula | C3H7NO2 |
| Molar mass | 89.09 g/mol |
| Appearance | White crystals or powder |
| Melting point | ≈300 ºC (dec.) |
| Water solubility | 167 g/L |
L-Serine fast facts
| CAS Reg. No. | 56-45-1 |
| Empirical formula | C3H7NO3 |
| Molar mass | 105.09 g/mol |
| Appearance | White crystals or powder |
| Melting point | 220–250 ºC (dec.) |
| Water solubility | 425 g/L |
MOTW update:
November 5, 2018
L-Alanine and L-Serine were the Molecules of the Week for October 29, 2018. They, along with glycine and L-proline, are the chief amino acids that make up spider silk proteins. In the past month, chemists at San Diego State University and Northwestern University (Evanston, IL) discovered that before spiders spin their silk, they store the silk proteins in complex nanoparticles.
MOTW update:
October 29, 2018
Skatole was the Molecule of the Week for March 5, 2012. It’s what causes mammalian feces to smell bad. Recently, scientists in China, Singapore, and the United States reported the discovery of the enzyme, indoleacetate decarboxylase, which bacteria use to convert tryptophan to skatole in the gut.
Learn more about this molecule from CAS, the most authoritative and comprehensive source for chemical information.
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