Glycine
Properties
| State | Solid (white crystalline powder) |
| Color | White |
| Solubility | Freely soluble in water (250 g/L at 25°C); insoluble in organic solvents |
| Melting Point | 233°C (decomposes) |
| Boiling Point | Decomposes before boiling |
About Glycine
Glycine is the smallest amino acid — H2N-CH2-COOH, molar mass 75.067 g/mol, the only one of the 20 proteinogenic residues whose side chain is just a hydrogen. That makes the alpha-carbon non-stereogenic and glycine optically inactive, the only achiral standard amino acid. The crystalline solid is one of the better-studied small biomolecules: it shows three polymorphs (alpha, beta, gamma) that differ only in hydrogen-bonding patterns, with the gamma form being the thermodynamically stable one and the alpha form what you actually get when crystallizing from neutral aqueous solution. The minimal side chain has two structural consequences: glycine fits into protein backbone positions where any other residue would clash sterically (the i+1 position in tight Type II beta-turns, the third position of every Gly-X-Y triplet in collagen's triple helix where it's pinned at the helix interior), and it grants the backbone unusual conformational flexibility — the Ramachandran plot for glycine residues covers nearly all of phi/psi space because there's no side chain to bump into the carbonyl oxygen. In the spinal cord and brainstem, glycine is the major fast inhibitory neurotransmitter, gating chloride influx through pentameric glycine receptors that are the molecular target of strychnine; in the cortex, glycine works the opposite way as an obligatory NMDA receptor co-agonist that has to bind the GluN1 subunit before glutamate can open the channel. In the lab, glycine is the workhorse buffer for SDS-PAGE running buffer (Tris-glycine-SDS), Western blot transfer buffer, and isoelectric focusing pH gradients — its three pKa values (2.34 carboxyl, 9.60 ammonium, pI 5.97) make it useful across an unusually wide pH range.
Where you'll encounter it
If you've ever cast an SDS-PAGE gel, eaten a gummy candy made from collagen-rich gelatin (which is about 21% glycine), or read a toxicology report on rodent strychnine poisoning, you've encountered glycine — Tris-glycine running buffer is the most-poured electrophoresis solution on the planet, and strychnine kills by competitively blocking glycinergic inhibition in the spinal cord, leaving every motor neuron firing at once. In a Western blot transfer setup, you make 1 L of transfer buffer by weighing out 14.4 g of glycine plus 3.0 g of Tris with 200 mL methanol, and the discontinuous pH gradient that results moves proteins from gel to PVDF in 90 minutes at 100 V. In an antibody-purification workflow eluting from a Protein A column, 0.1 M glycine·HCl at pH 2.5 strips bound IgG into a quenching tube of 1 M Tris pH 9 — fast, mild, and reproducible across thousands of antibody preps daily.
Common Uses
- Tris-glycine running buffer for SDS-PAGE protein electrophoresis
- Major fast inhibitory neurotransmitter in spinal cord and brainstem
- Obligatory co-agonist at NMDA receptor GluN1 subunit
- Building block in collagen triple-helix Gly-X-Y repeat (every third residue)
- Sweetener and bacteriostatic agent in food preservation (E640)
- Substrate for porphyrin synthesis via ALA-synthase (heme biosynthesis pathway)
- Buffer for protein elution from antibody affinity columns (0.1 M, pH 2.5-3.0)
- Precursor for industrial glyphosate herbicide production
Safety Information
GRAS for food and pharmaceutical use; oral LD50 in rats is 7.93 g/kg. No GHS hazard classification. Practical concerns are minimal: bulk handling generates fine dust that's a nuisance more than a hazard, and intravenous glycine irrigation fluid used during transurethral prostatectomy can cause 'TURP syndrome' if absorbed in large volumes (hyponatremia plus glycine-derived ammonia toxicity from glyoxylate metabolism). Industrial glycine is non-corrosive, non-flammable, and non-reactive with common solvents; standard lab PPE (gloves, dust mask if weighing kilograms) is sufficient. Don't confuse with glyphosate (Roundup), which is N-(phosphonomethyl)glycine and has a completely different toxicology profile.
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.