The AtlasAmino acidsPolar, uncharged
ThreonineThr · T
An essential amino acid that the gut keeps most of for itself, built into the mucus that lines it, and whose main enzyme in other mammals is broken in us.
Molecule · Thr · 8 heavy atoms
Threonine
C4H9NO3119.12 g/mol
An essential amino acid that the gut keeps most of for itself, built into the mucus that lines it, and whose main enzyme in other mammals is broken in us.
Built fromthe charted ones open their own entry
- Codes
- Thr · T
- Formula
- C4H9NO3
- Molar mass
- 119.12 g/mol
- Systematic name
- (2S,3R)-2-amino-3-hydroxybutanoic acid
- Side chain
- 1-Hydroxyethyl: a carbon carrying a hydroxyl and a methyl; polar and uncharged.
- Class
- Polar, uncharged
- In the diet
- Essential
- Carbon skeleton
- Glucogenic and ketogenic
- pKa
- α-COOH 2.11 · α-NH3+ 9.62
- Isoelectric point
- pH 5.87
- Hydropathy
- -0.7 (Kyte–Doolittle)
- Codons
ACUACCACAACG
pKa and isoelectric point: Nelson and Cox, Lehninger Principles of Biochemistry, table of amino acid properties (free amino acid, 25 °C). Hydropathy: Kyte and Doolittle, J Mol Biol 1982. Essentiality: Reeds, J Nutr 2000. Formula and mass computed from the structure.
In brief
What it is
An essential amino acid with a small side chain carrying a hydroxyl group and a methyl group, which gives it a second stereocentre 1. It is one of the three amino acids that are phosphorylated to switch proteins on and off 2.
Why it matters
The gut takes most of it: in preterm infants 70 to 82% of dietary threonine was used by the intestine on first pass, largely to make mucins, the proteins of the mucus layer, whose cores are rich in threonine, serine and proline 3,4.
Where it runs short
In rats on 30% of their threonine requirement for two weeks, mucin synthesis fell in the small and large intestine while other gut protein synthesis did not; at 60% there was no difference 5.
Where it turns
Threonine is a precursor of propionate, so it is restricted, along with methionine, valine and isoleucine, in methylmalonic and propionic acidemia 6.
The intestine is first in line for threonine, and the first place a severe shortfall shows.
The molecule
Threonine is like serine with an extra methyl group: a two-carbon side chain with a hydroxyl on the first carbon. That hydroxyl is where sugars are attached in mucins and where kinases attach phosphate; a 2006 survey of signaling in human cells mapped 6,600 phosphorylation sites on 2,244 proteins 2,4.
The extra methyl creates a second stereocentre on the side chain, so threonine and isoleucine are the two standard amino acids with two.
StereochemistryThreonine has two stereocentres, so it has four forms; the one in protein is (2S,3R). Its diastereomer, allo-threonine, is not used to build protein.
Move across the chart to read the charge at any pH.
Computed from its pKa values (α-carboxyl 2.11, α-amino 9.62) by the Henderson–Hasselbalch equation, for the free amino acid in water at 25 °C. Inside a folded protein the same groups can shift by a unit or more. The faint lines are the other amino acids.
Kyte–Doolittle hydropathy index: positive values avoid water and tend to be buried inside a folded protein, negative values sit on its surface. Each letter is an amino acid; choose one to open it.
| 1st ↓ 2nd → | U | C | A | G | 3rd |
|---|---|---|---|---|---|
| U | UUUPhe | UCUSer | UAUTyr | UGUCys | U |
| UUCPhe | UCCSer | UACTyr | UGCCys | C | |
| UUALeu | UCASer | UAAStop | UGAStop | A | |
| UUGLeu | UCGSer | UAGStop | UGGTrp | G | |
| C | CUULeu | CCUPro | CAUHis | CGUArg | U |
| CUCLeu | CCCPro | CACHis | CGCArg | C | |
| CUALeu | CCAPro | CAAGln | CGAArg | A | |
| CUGLeu | CCGPro | CAGGln | CGGArg | G | |
| A | AUUIle | ACUThr | AAUAsn | AGUSer | U |
| AUCIle | ACCThr | AACAsn | AGCSer | C | |
| AUAIle | ACAThr | AAALys | AGAArg | A | |
| AUGMet | ACGThr | AAGLys | AGGArg | G | |
| G | GUUVal | GCUAla | GAUAsp | GGUGly | U |
| GUCVal | GCCAla | GACAsp | GGCGly | C | |
| GUAVal | GCAAla | GAAGlu | GGAGly | A | |
| GUGVal | GCGAla | GAGGlu | GGGGly | G |
Where it comes from
Threonine is essential; the adult requirement is 15 mg per kilogram a day 1. Microbes and plants make it as part of the aspartate family, alongside lysine, methionine and isoleucine 7.
Almost all of it is made by bacterial fermentation, and almost none of it is for people. Industrial L-threonine is produced by genetically modified Escherichia coli and sold as a feed additive for every animal species; the 2026 European assessment of one such product describes the process, notes that the production cells are inactivated but not removed, and is the kind of document that says plainly what a supplement label does not 8.
EssentialMust come from food; the adult requirement is 15 mg per kilogram a day 1.
How much
15 mg per kilogram a day for adults 1.
Where it is in food
- Any protein; whey glycomacropeptide is unusually rich in it 9.
In the bottle · fermentedOne of the three amino acids made in the largest amounts by fermentation, in engineered Escherichia coli or Corynebacterium glutamicum, for feed, food and medicine 7,10.
What the body does with it
The intestine is threonine’s main consumer. In preterm infants on partial and full feeds, 82% and 70% of dietary threonine was taken up by the gut on first pass 3; in piglets the gut used 85 to 91%, mostly to build its own mucosal proteins 11.
Much of that goes into mucins. MUC2, the main gel-forming mucin of the intestine, has long domains rich in proline, threonine and serine that carry the dense sugar chains making up more than half its weight, and in mice the inner colonic mucus layer is renewed about every hour 4.
In mouse embryonic stem cells threonine has a role it does not have in us. These cells depend on threonine more than on any other amino acid, breaking it down by threonine dehydrogenase into glycine and acetyl-CoA to feed the methyl donor S-adenosylmethionine and maintain histone methylation 12,13. The human version of the gene is an expressed pseudogene, truncated by a stop codon and a lost splice site in every person genotyped 14.
The stem-cell story has a correction worth recording. Mouse embryonic stem cells break threonine down with threonine dehydrogenase to feed one-carbon units into S-adenosylmethionine, and the enzyme was reported to control trimethylation of histone H3 at lysine 4 and so cell fate. Taken into a live animal, the second half did not follow: in zebrafish hematopoiesis tdh turns out to be expressed mainly in neutrophils, and knocking it out lowers neutrophil numbers and blunts their response to injury WITHOUT changing H3K4me3 15. A mechanism that works in a dish is a hypothesis about an animal, and this one was tested.
In collagen, threonine can stand in for a modification it has no business imitating. Collagen's stability comes from 4-hydroxyproline, made after the protein is built and never removed. In synthetic collagen-mimetic peptides, replacing the proline of a central Pro-Hyp-Gly triplet with serine, threonine or their phosphorylated forms destabilized the helix in every case but one: phosphothreonine in the second position preserved it 16. Phosphorylation is reversible and hydroxylation is not, which makes it the first candidate for a collagen modification a cell could switch off again.
In three sentences each
Kept by the gut
Most dietary threonine never leaves the intestine: 70 to 82% in preterm infants and 85 to 91% in piglets, mainly built into the gut lining’s own proteins 3,11.
The backbone of mucus
Mucins are more than half sugar by weight, attached to protein regions rich in proline, threonine and serine; the sugars hang from the hydroxyls of threonine and serine 4.
How it is made, moved and broken down
Because the human dehydrogenase is broken, threonine is mostly broken down by serine–threonine dehydratase, a vitamin B6 enzyme, to α-ketobutyrate and then propionyl-CoA 17,18. Propionyl-CoA is where valine, isoleucine, methionine and odd-chain fats also meet, which is why threonine counts as a precursor in the propionate disorders 6.
Carbon skeleton · glucogenic and ketogenicMainly broken down by serine–threonine dehydratase to α-ketobutyrate and on to propionyl-CoA, which can make glucose; the minor dehydrogenase route yields glycine and acetyl-CoA 12,17,18.
- Threonine
- Serine–threonine dehydrataseSDS · vitamin B6
- α-Ketobutyrate
- Branched-chain ketoacid dehydrogenaseBCKDHA · thiamine, lipoate
- Propionyl-CoA
- Threonine
- Threonine dehydrogenaseTDH (pseudogene) · NAD⁺
- 2-Amino-3-ketobutyrate
- Glycine C-acetyltransferaseGCAT · vitamin B6
- Glycine + acetyl-CoA
Where it matters most
When it goes wrong
Inherited
Methylmalonic and propionic acidemia
MMUT, PCCA, PCCB · autosomal recessive
Threonine is one of the four amino acids whose breakdown feeds propionyl-CoA, so the diet restricts natural protein, and special amino acid mixtures free of those precursors are used 6.
How it is foundNewborn screening and plasma acylcarnitines, then organic acids 6.
Drug
Spasticity
In 26 people with multiple sclerosis, 7.5 g a day reduced signs of spasticity on examination without improving symptoms 19; a sequential trial in spinal spasticity found a modest effect 20. A Cochrane review of anti-spasticity agents made no recommendation 21.
Drug
ALS
Threonine and branched-chain amino acids were tried in motor neurone disease without benefit 22.
How it is measured
Plasma threonine is measured in the amino acid panel 23. It has a niche use as an adherence marker in PKU, because glycomacropeptide, a whey protein used in low-phenylalanine formulas, contains two to three times more threonine than other proteins 9.
Low plasma threonine has been looked at as a prognostic marker and has not earned the role. A secondary analysis of the EFFORT trial measured lysine, methionine and threonine in 237 malnourished medical inpatients, 58 of whom died within 30 days: low methionine predicted death (adjusted HR 1.98, 95% CI 1.16 to 3.36) and functional decline, and lysine and threonine showed nothing 24. The threonine result is the useful one here precisely because it is null — the three were measured together, by one group, in one trial, and only one of them mattered.
In liver disease it moves as part of a trio rather than alone. Plasma free amino acids from 23,036 people with steatosis data in a Japanese biobank, including 310 with metabolic dysfunction-associated steatotic liver disease, point at glycine–serine–threonine metabolism as the disturbed pathway rather than at any single one of the three 25.
Food, supplements and the evidence
Establishedreplicated in people, for a named outcome
- Threonine restriction, as part of precursor restriction, in methylmalonic and propionic acidemia 6.
- Supplemental L-threonine is well tolerated up to 12 g a day in healthy adults. A randomized, double-blind crossover trial gave 0, 3, 6, 9 and 12 g a day for four weeks each and found no effect on anthropometry, dietary intake or biochemistry except a minor, non-specific rise in aspartate aminotransferase and creatine kinase at 9 g that did not appear at 12 g; the no-observed-adverse-effect level was set at 12 g a day 26. Tolerated is not the same as useful, and the trial was in healthy men.
Uncertainsmall, short, mixed, surrogate or preclinical
- Threonine for gut barrier health: the mucin effect is shown in animals at severe deficiency, not in people eating normal diets 5,27.
- Threonine for spasticity: small trials, modest signs, no symptomatic benefit 19,20,21.
- How much threonine anyone actually needs. The 15 mg per kilogram figure comes from indicator amino acid oxidation, and the method's main criticism — that a one-day adaptation is too short — has now been tested directly: eleven men studied at six intakes with one, three or seven days of adaptation gave the same requirement either way 28. What remains open is who it applies to. A 2025 systematic review screening 11,408 studies found that the dietary reference intakes have not been updated since 2005, and that the adult threonine requirement rests on studies in men only 29.
Sold asthe claim on the label, against the evidence
- “Magnesium L-threonate for sleep.” The threonate is threonine's oxidized form, used as a carrier because it is said to get magnesium into the brain, and the product is sold for sleep. In 100 adults with self-reported dissatisfied sleep, six weeks of 2 g a day beat placebo on a cognition composite (P = 0.043), on reaction time (P = 0.031) and on self-reported sleep-related impairment (P = 0.043) — and did not differ from placebo on sleep disturbance (P = 0.316), restorative sleep (P = 0.439), general wellbeing (P = 0.436) or on any sleep measure from the ring the participants were wearing 30. A second trial put 2 g of magnesium L-threonate with L-theanine and apigenin in an evening arm against a morning adaptogen arm, both together, and placebo, in 103 healthy adults: every significant improvement in stress, affect and sleep belonged to the MORNING arm, and the combined arm did worse than the morning arm alone on sleep quality 31. The ingredient's own best evidence is for cognition, not for the thing on the front of the box.
What is strange about it
In humans, the gene for threonine’s main mammalian breakdown enzyme is still transcribed in every tissue, but it cannot make a working protein 14. Parasites such as trypanosomes have a working version, which makes it a possible drug target precisely because we lack it 32.
Threonine was tried in the 1990s for spasticity in multiple sclerosis and spinal disease; the trials found modest effects on examination without patients feeling better, and a Cochrane review made no recommendation 19,20,21.
In mice, the inner mucus layer of the colon, built on threonine-rich mucin, is replaced about every hour 4.
Where it connects
In the Atlas
Topics on the map
On the map
A star in The essential amino acids, one of 14. Gut mucus is unusually rich in it, and a large share of dietary threonine is used by the gut wall before the rest of the body sees any.
Sources
32 sources, numbered as they are cited. Every one was checked against PubMed or its publisher before it was cited here; the note under each says what it shows and what it does not.
- 1Joint WHO/FAO/UNU Expert Consultation. Protein and amino acid requirements in human nutrition.PMID 18330140
Threonine, 15 mg/kg/day.
- 2Olsen JV, Blagoev B, Gnad F, et al. Global, in vivo, and site-specific phosphorylation dynamics in signaling networks.doi:10.1016/j.cell.2006.09.026 · PMID 17081983
6,600 phosphorylation sites on 2,244 proteins.
- 3van der Schoor SRD, Wattimena DL, Huijmans J, et al. The gut takes nearly all: threonine kinetics in infants.doi:10.1093/ajcn/86.4.1132 · PMID 17921393
Eight preterm infants; first-pass gut uptake 82% and 70%.
- 4Johansson MEV, Hansson GC. Immunological aspects of intestinal mucus and mucins.doi:10.1038/nri.2016.88 · PMID 27498766
Mucin structure; MUC2; renewal of the inner layer in mice.
- 5Faure M, Moënnoz D, Montigon F, et al. Dietary threonine restriction specifically reduces intestinal mucin synthesis in rats.doi:10.1093/jn/135.3.486 · PMID 15735082
Rats, two weeks; effect at 30% of requirement, not at 60%. Industry-funded.
- 6Forny P, Hörster F, Ballhausen D, et al. Guidelines for the diagnosis and management of methylmalonic acidaemia and propionic acidaemia: first revision.doi:10.1002/jimd.12370 · PMID 33595124
Threonine among the propionate precursors.
- 7Li Y, Wei H, Wang T, et al. Current status on metabolic engineering for the production of L-aspartate family amino acids and derivatives.doi:10.1016/j.biortech.2017.05.145 · PMID 28579173
The aspartate family: lysine, methionine, threonine, isoleucine.
- 8EFSA Panel on Additives and Products or Substances used in Animal Feed (FEEDAP); Villa RE, Azimonti G, et al. Safety and efficacy of a feed additive consisting of l-threonine produced using Escherichia coli KCCM 80367 for all animal species.doi:10.2903/j.efsa.2026.10294 · PMID 42741374
Where almost all industrial threonine goes, and the regulatory file that says how it is made.
- 9Ney DM, Stroup BM, Clayton MK, et al. Glycomacropeptide for nutritional management of phenylketonuria: a randomized, controlled, crossover trial.doi:10.3945/ajcn.116.135293 · PMID 27413125
30 people; plasma threonine rose on glycomacropeptide.
- 10Zhao G, Zhang D, Tang Y, et al. Recent advances on engineering Escherichia coli and Corynebacterium glutamicum for efficient production of L-threonine and its derivatives.doi:10.1016/j.ymben.2025.02.012 · PMID 40020772
One of the three major fermented amino acids.
- 11Schaart MW, Schierbeek H, van der Schoor SRD, et al. Threonine utilization is high in the intestine of piglets.doi:10.1093/jn/135.4.765 · PMID 15795432
Piglets; gut used 85–91% of dietary threonine.
- 12Wang J, Alexander P, Wu L, et al. Dependence of mouse embryonic stem cells on threonine catabolism.doi:10.1126/science.1173288 · PMID 19589965
Mouse cells; threonine dehydrogenase to glycine and acetyl-CoA.
- 13Shyh-Chang N, Locasale JW, Lyssiotis CA, et al. Influence of threonine metabolism on S-adenosylmethionine and histone methylation.doi:10.1126/science.1226603 · PMID 23118012
Mouse stem cells; threonine feeds SAM and H3K4 trimethylation.
- 14Edgar AJ. The human L-threonine 3-dehydrogenase gene is an expressed pseudogene.doi:10.1186/1471-2156-3-18 · PMID 12361482
Truncated in all 23 people genotyped.
- 15Li NZ, Wang ZX, Zhang F, et al. Threonine dehydrogenase regulates neutrophil homeostasis but not H3K4me3 levels in zebrafish.doi:10.1111/febs.17138 · PMID 38652546
The stem-cell epigenetic story, taken into a living animal, where it did not hold.
- 16Pearl IMB, Raines RT. Threonine phosphorylation is a bioreversible surrogate of proline hydroxylation in a collagen triple helix.doi:10.1021/jacs.5c19090 · PMID 42424232
A modification the cell can take off again, doing the job of one it cannot.
- 17Darling PB, Grunow J, Rafii M, et al. Threonine dehydrogenase is a minor degradative pathway of threonine catabolism in adult humans.doi:10.1152/ajpendo.2000.278.5.E877 · PMID 10780944
Six men; 7–11% of breakdown.
- 18Tong H, Davis L. Cofactor identification of threonine-serine dehydratase from sheep liver.doi:10.1006/prep.1993.1058 · PMID 8251757
Sheep enzyme: threonine to α-ketobutyrate; vitamin B6 cofactor.
- 19Hauser SL, Doolittle TH, Lopez-Bresnahan M, et al. An antispasticity effect of threonine in multiple sclerosis.doi:10.1001/archneur.1992.00530330045014 · PMID 1520082
26 patients, crossover, 7.5 g/day.
- 20Lee A, Patterson V. A double-blind study of L-threonine in patients with spinal spasticity.doi:10.1111/j.1600-0404.1993.tb05353.x · PMID 8296531
6 g/day; sequential design, 33 patients.
- 21Shakespeare DT, Boggild M, Young C. Anti-spasticity agents for multiple sclerosis.doi:10.1002/14651858.CD001332 · PMID 14583932
No recommendation.
- 22Parton M, Mitsumoto H, Leigh PN. Amino acids for amyotrophic lateral sclerosis/motor neuron disease.doi:10.1002/14651858.CD003457 · PMID 14583978
No benefit; review later withdrawn (2008).
- 23Xia T, Gao S, Shu C, et al. Analysis of amino acids in human blood using UHPLC-MS/MS: potential interferences of storage time and vacutainer tube in pre-analytical procedure.doi:10.1016/j.clinbiochem.2016.09.018 · PMID 27693603
Pre-analytical effects.
- 24Wunderle C, Haller L, Laager R, et al. The association of the essential amino acids lysine, methionine, and threonine with clinical outcomes in patients at nutritional risk: secondary analysis of a randomized clinical trial.doi:10.3390/nu16162608 · PMID 39203745
237 inpatients at nutritional risk. Methionine predicted death; threonine did not.
- 25Mino M, Kakazu E, Sano A, et al. Comprehensive analysis of peripheral blood free amino acids in MASLD: the impact of glycine–serine–threonine metabolism.doi:10.1007/s00726-024-03433-2 · PMID 39718621
23,036 people with steatosis data, 310 with the diagnosis.
- 26Matsumoto H, Miura N, Naito M, et al. Evaluation of safe utilization of L-threonine for supplementation in healthy adults: a randomized double blind controlled trial.doi:10.1007/s00726-025-03461-6 · PMID 40419835
The first graded-dose safety trial in people: 0, 3, 6, 9 and 12 g a day for four weeks, crossover.
- 27Nichols NL, Bertolo RF. Luminal threonine concentration acutely affects intestinal mucosal protein and mucin synthesis in piglets.doi:10.1093/jn/138.7.1298 · PMID 18567751
Piglet gut loops; total mucosal protein synthesis also fell.
- 28Szwiega S, Pencharz PB, Ball RO, et al. Length of adaptation has no effect on the threonine requirement determined in healthy young adult males using the indicator amino acid oxidation method.doi:10.1016/j.tjnut.2023.03.033 · PMID 37004875
The criticism of the method, tested against itself: one day of adaptation gave the same answer as seven.
- 29Burstad KM, Lamina T, Erickson A, et al. Evaluation of dietary protein and amino acid requirements: a systematic review.doi:10.1016/j.ajcnut.2025.04.017 · PMID 40610129
11,408 studies screened, 66 usable, and the adult threonine requirement rests on men.
- 30Lopresti AL, Smith SJ. The effects of magnesium L-threonate (Magtein) on cognitive performance and sleep quality in adults: a randomised, double-blind, placebo-controlled trial.doi:10.3389/fnut.2025.1729164 · PMID 41601871
100 adults with dissatisfied sleep, six weeks, 2 g a day, with a wearable measuring the thing the product is sold for.
- 31Mastrofini GF, Romersi RF, Lombardi MG, et al. Modulating stress and sleep through a multi-compound dietary supplement: a randomized, double-blind, placebo-controlled trial.doi:10.1080/15502783.2026.2740227 · PMID 42829807
Four arms, so the evening stack could be judged against the morning one and against both together.
- 32Adjogatse E, Erskine P, Wells SA, et al. Structure and function of L-threonine-3-dehydrogenase from the parasitic protozoan Trypanosoma brucei revealed by X-ray crystallography and geometric simulations.doi:10.1107/S2059798318009208 · PMID 30198897
The parasite enzyme as a drug target.
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