Alanine
Properties
| State | Solid (white crystalline powder) |
| Color | White |
| Solubility | Soluble in water (166 g/L at 25°C); slightly soluble in ethanol |
| Melting Point | 258°C (decomposes) |
| Boiling Point | Decomposes before boiling |
About Alanine
Alanine is the second-smallest of the twenty proteinogenic amino acids and the simplest one with a chiral α-carbon — the side chain is just a methyl group, the smallest substituent that still gives the molecule a defined L versus D configuration. That smallness is the entire point of why alanine matters as a research tool: in alanine-scanning mutagenesis, biochemists systematically replace candidate functional residues in a protein with alanine, and any drop in activity that results is attributed to the original side chain rather than to general structural disruption. The methyl group occupies essentially the same volume as the β-carbon of any standard amino acid, so the backbone geometry is preserved while the side-chain chemistry (charge, hydrogen-bonding, hydrophobic bulk beyond a methyl) is wiped out. In structural biology, alanine residues are also overrepresented in α-helices because the small nonpolar side chain doesn't interfere with the helical hydrogen-bond pattern that runs along the backbone. The molecule sits at the center of nitrogen metabolism through the glucose-alanine cycle: working muscle transaminates pyruvate (the glycolysis output) to alanine using glutamate as the amino donor, ships the alanine through the bloodstream to the liver, where it gets transaminated back to pyruvate for gluconeogenesis and the amino group enters the urea cycle. The pathway is the body's main way of moving nitrogen out of contracting muscle without releasing free ammonia.
Where you'll encounter it
If you've taken a structural-biology or protein-engineering course, alanine is the residue you've worked with most explicitly — it's the default mutation in a scanning study, the standard residue used to neutralize a charged or polar side chain when probing function. In sports nutrition, alanine shows up as β-alanine (the β isomer, where the amino group is on the β-carbon rather than the α), which is sold as a supplement because it's the rate-limiting precursor to carnosine in muscle and is reported to delay fatigue in high-intensity exercise. The α-alanine that appears in proteins isn't typically supplemented because the body makes plenty from pyruvate transamination on demand. The two enantiomers, L- and D-alanine, both occur in nature: L-alanine in proteins, D-alanine as a structural component of bacterial cell-wall peptidoglycan, which is why penicillin and vancomycin (both of which target D-Ala-D-Ala motifs) can be selectively toxic to bacteria.
Common Uses
- Default substitution in alanine-scanning mutagenesis
- Standard residue for stabilizing α-helical model peptides
- Substrate for ALT (alanine aminotransferase) clinical assays
- Component of total parenteral nutrition formulations
- Reference compound for chiral chromatography and circular dichroism
Safety Information
GRAS (generally recognized as safe) for food and supplement use. No GHS hazard classification for routine handling. The only practical consideration is hygroscopicity — solid alanine pulls moisture from humid air and clumps in long-term storage, so keep desiccated.
This safety summary is for educational reference only and may not be complete. It is not a substitute for Safety Data Sheets (SDS), medical advice, or professional chemical safety guidance. Always consult appropriate SDS and qualified professionals before handling chemicals.