Lysine is one of the standard amino acids that make up proteins, and it also occurs on its own, unattached, in foods, feeds, fermentation samples, and cell culture media. A lab reports it as part of a wider profile, not in isolation. Lysine comes up often in feed and pet food work, where it is discussed as a limiting amino acid in some diets: the amino acid in shortest supply relative to the animal's need, in that formulation context. That context explains why people ask for a lysine number. It does not supply one, and this page gives no typical content for any feed, food, or material.
Chemistry in plain terms
Standard references classify lysine as an essential amino acid for humans, meaning it must come from food rather than being made by the body in sufficient amounts. Lysine is also classed among the basic amino acids: beyond the usual amino and carboxylic acid groups, its side chain carries an additional amino group. PubChem lists L-lysine as a standard proteinogenic amino acid, built into protein chains as well as present free in solution. Both forms, bound and free, are real, and they answer different questions.
Because lysine appears both bound in protein and present free in some formulations, the basis matters. A number without its basis, free or total, is easy to misread.
Where it occurs
Lysine occurs as a building block in proteins across foods, feeds, and biological materials. Free lysine also occurs in cell culture and spent media, fermentation liquids, protein hydrolysates, animal feeds and pet foods, and food and supplement products, where a free profile describes the sample as it is.
This page gives no typical level for lysine in any material, feed, or food. Levels vary by recipe, ingredients, organism, process, and sampling point; no verified figure is available. Measure your sample rather than borrowing a number.
Free vs total for lysine
A free lysine result measures lysine already dissolved and unattached in the sample as received, with no hydrolysis step. That is usually the relevant number for a question about the sample as used or as eaten: what is in the medium now, or what free profile a feed or product presents.
A total result is measured after acid hydrolysis, the step that breaks protein chains apart and releases bound amino acids. It therefore includes free lysine plus lysine bound inside protein. This page gives no free-to-total ratio for any material, because that ratio is a property of the specific sample.
Lysine has no special hydrolysis conversion of the kind that affects asparagine and glutamine, whose amide groups are lost during acid hydrolysis and which are therefore reported together with aspartic acid and glutamic acid respectively. The general total-panel caution still applies: a hydrolysed measurement describes the sample after the method has acted on it, not a photograph of its native state.
Method notes: how lysine is measured here
At OpenChemWorks, lysine is measured as part of a panel using AQC pre-column derivatization, the Waters AccQ-Tag approach, with HPLC-UV detection. The amino acids are chemically tagged, separated on the HPLC column, and quantified against calibrated standards. AABA, short for alpha-aminobutyric acid, is added at a known amount as the internal standard. AABA is the standard, added by the lab; lysine is the analyte, measured from your sample. Different compounds, different roles.
No resolution, recovery, or detection-limit figure is quoted here, because no verified figure from this laboratory's validated method is available.
Which panel includes lysine
Lysine is included in AA-1, the free amino acid panel: 19 amino acids plus ammonia, measured by AQC HPLC-UV. Cysteine is excluded from AA-1 and needs a separate AA-3 workup. Lysine is also part of a total result under AA-T, where the sample is hydrolysed first and lysine is reported on that total basis.
Prices are only these: AA-1 costs $150 per sample for liquids, $180 per sample for powders ($150 plus $30 powder preparation), and $150 flat for first-time customers, with $125 per sample at 25 or more samples per month. AA-T, total amino acid analysis, costs $230 per sample. The pilot is $250 for 5 samples, credited in full against a first contract signed within 90 days.
OpenChemWorks, in Davis, California, is validating now and reserving pilot slots. The lab is not GLP, GMP, or ISO/IEC 17025 accredited, and no turnaround is promised here. Email info@openchemworks.com with your sample description and whether your question is about the sample as it is, or its protein as a whole.
Frequently asked questions
Why do feed and pet food makers ask about lysine?
Lysine is discussed in formulation work as a limiting amino acid in some diets, so its measured level in a specific feed is a formulation input. This page gives no typical value; your feed's level has to be measured.
Is AABA the same as lysine?
No. AABA, alpha-aminobutyric acid, is the internal standard added by the lab for quantification. Lysine is a different compound, and it is the analyte measured from your sample.
Do I need free or total lysine?
Free answers a question about the sample as received. Total answers a question about protein composition after hydrolysis, and includes the free fraction.
Is lysine reported on its own?
At OpenChemWorks it is reported as part of the AA-1 free panel or the AA-T total panel, alongside the other panel analytes.
References
- PubChem — L-Lysine (CID 5962) — Identity reference for the amino acid named on this page.
- Waters — Derivatization of Amino Acids Using Waters AccQ-Tag Chemistry — Method background for AQC derivatization and HPLC-UV amino acid analysis.
- British Journal of Nutrition (2023) — Asparagine and glutamine lose an amide residue during acid hydrolysis and are measured with aspartate and glutamate respectively.
- OpenChemWorks — Pricing — Published service and pricing copy (2026).
OpenChemWorks Laboratory · Reviewed by the laboratory director, PhD chemist · Published October 29, 2026