Lysine
Properties
| State | Solid (white crystalline powder) |
| Color | White |
| Solubility | Highly soluble in water (freely soluble); slightly soluble in ethanol |
| Melting Point | 224 °C (decomposes) |
| Boiling Point | Decomposes before boiling |
About Lysine
Lysine, three-letter Lys and one-letter K, is the amino acid whose side chain is a four-carbon tether ending in a primary amine. The side-chain pKa sits around 10.5, so at physiological pH the epsilon-NH3+ carries a full positive charge — and that single feature drives most of what lysine does in biology. Histone tails are Lys-rich precisely because that string of cations grips the phosphate backbone of DNA; flip those Lys side chains from charged to acetylated (HDAC and HAT enzymes do this dynamically) and the chromatin loosens, transcription opens up. Methylation at H3K4 versus H3K9 versus H3K27 means completely different things to a cell, and reading those marks is the day job of bromodomain and chromodomain proteins. In collagen, lysyl oxidase oxidatively deaminates specific Lys and hydroxylysine residues to allysine; the resulting aldehydes then condense into the trivalent cross-links that give skin and tendon their tensile strength — defective lysyl oxidase is what makes a copper-deficient diet produce floppy connective tissue. Lysine also matters at the dinner table: it is the first limiting amino acid in wheat, rice, and corn, which is why the rice-and-beans, wheat-and-lentils, corn-and-bean pairings that emerged independently across cultures all hit the same biochemical target. Industrially, L-lysine is fermented from glucose by Corynebacterium glutamicum at megaton scale for animal feed.
Where you'll encounter it
If you have ever supplemented a vegetarian diet with legumes, fed a pig or chicken on a corn-based ration, or pulled a Western blot probing for an acetyl-K mark on histone H3, you have been working with lysine biochemistry directly. Swine and poultry nutritionists run feed formulations on a 'standardized ileal digestible lysine' basis precisely because Lys is the first limiting amino acid in corn and soybean rations — drop synthetic L-lysine HCl by 0.1% and growth rate stalls within a week. Epigenetics researchers ordering H3K9me3 or H3K27ac antibodies from Cell Signaling are buying reagents that distinguish methyl from acetyl marks on the same Lys residue, and the choice between H3K4me3 (active promoter) and H3K9me3 (heterochromatin) drives the entire interpretation of a ChIP-seq experiment.
Common Uses
- Animal-feed supplement (L-lysine HCl), produced at roughly 2.5 million tonnes per year by C. glutamicum fermentation
- Essential dietary amino acid, first limiting in wheat, rice, and corn
- Substrate for histone acetylation and methylation marks studied in epigenetics
- Substrate for lysyl oxidase in collagen and elastin cross-link formation
- L-lysine HCl supplements (1-3 g/day) marketed for cold-sore prophylaxis
- Building block in solid-phase peptide synthesis using Fmoc-Lys(Boc)-OH
Safety Information
GRAS for food and feed use. Free L-lysine and L-lysine HCl are well tolerated at supplementation doses of 1 to 3 g per day; gram-scale boluses can produce GI cramping or osmotic diarrhea. Sustained intakes above roughly 6 g/day have been linked to reduced renal arginine reabsorption in case reports. Not classified under GHS. The DL-mixture and the unnatural D-enantiomer have no nutritional value and should not be used in feed.
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.