The AtlasAmino acidsPolar, uncharged

AsparagineAsn · N

The amide of aspartate: the anchor for sugars on proteins, the amino acid childhood leukaemia is starved of, and the precursor of the acrylamide in chips.

Status Reference · not yet an episodeSources 21Reviewed October 2026

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Skeletal formula — every corner and every line end is a carbon, and the hydrogens on carbon are left implied.

Molecule · Asn · 9 heavy atoms

Asparagine

C₄H₈N₂O₃132.12 g/mol

The amide of aspartate: the anchor for sugars on proteins, the amino acid childhood leukaemia is starved of, and the precursor of the acrylamide in chips.

Built fromthe charted ones open their own entry

C4CarbonH8Hydrogen N2Nitrogen O3Oxygen

Codes: Asn · N
Formula: C₄H₈N₂O₃
Molar mass: 132.12 g/mol
Systematic name: (2S)-2,4-diamino-4-oxobutanoic acid
Side chain: Carbamoylmethyl: one carbon and an amide; polar and uncharged.
Class: Polar, uncharged
In the diet: Dispensable
Carbon skeleton: Glucogenic
pKa: α-COOH 2.02 · α-NH₃⁺ 8.80
Isoelectric point: pH 5.41
Hydropathy: -3.5 (Kyte–Doolittle)
Codons: AAU AAC

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

Aspartate with its side-chain acid turned into an amide: a short, polar, uncharged side chain. The body makes it from aspartate and glutamine with asparagine synthetase ¹.

Why it matters

Asparagine is where most sugars are attached to proteins, at Asn-X-Ser/Thr sequences ². Leukaemic lymphoblasts depend on it from the blood, which is why asparaginase, an enzyme that destroys it, is a core drug for childhood acute lymphoblastic leukaemia ^3,4.

Where it runs short

The brain needs to make its own: children with asparagine synthetase deficiency are born with small heads and develop seizures and progressive brain atrophy, while other organs are spared ^1,5.

Where it turns

In food, heated with reducing sugars above about 120 °C, asparagine is the main source of acrylamide, a probable human carcinogen, in fried potatoes and baked cereals ^6,7.

In the body the risk is too little; in the frying pan, too much.

The molecule

Asparagine is aspartate with its side-chain carboxylic acid replaced by an amide. The amide is polar but uncharged, and can both give and accept hydrogen bonds.

That amide is not permanent. In proteins asparagine slowly loses it, deamidating to aspartate or isoaspartate, at a rate set by its neighbours; measured across 306 sequences, the rates vary enough that deamidation has been proposed as a built-in molecular timer of protein age ⁸. A repair enzyme handles the damage, and mice without it die young ⁹.

Charge · pHAsparagine carries almost no net charge at the pH of blood.

Move across the chart to read the charge at any pH.

Computed from its pKa values (α-carboxyl 2.02, α-amino 8.80) 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.

HydropathyAsparagine scores -3.5: the 6th most water-loving of the twenty.

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.

The genetic codeAsparagine has 2 codons. The code is redundant, so most single-letter changes at the third position still write asparagine.

The 64 codons of the standard genetic code. Codons for asparagine are marked.
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

Asparagine synthetase makes asparagine from aspartate, taking the amide nitrogen from glutamine and spending ATP. It is present in most organs but at very different levels, and its expression rises sharply under cellular stress, through a single gene on chromosome 7 ¹.

The brain is the one organ that cannot do without it: inherited loss of the enzyme damages the developing brain while leaving other organs normal ⁵.

DispensableMade from aspartate and glutamine by asparagine synthetase, present in most organs; the brain depends on its own synthesis ^1,5.

How much

None; the body makes it ¹.

Where it is in food

Potatoes and cereals are rich in free asparagine, which is why they form the most acrylamide when fried or baked ⁶.

In the bottle · synthetic or enzymaticAsparagine is made by low-yield extraction from plants, by chemical synthesis, or increasingly with asparagine synthetase in engineered bacteria, coupled to systems that regenerate ATP ¹⁰.

What the body does with it

Asparagine is the attachment point for N-linked sugars. The chains are assembled on a lipid carrier and then transferred en bloc to asparagines in the sequence Asn-X-Ser/Thr; this is essential in all eukaryotes and shapes how most secreted and membrane proteins fold and work ².

In cancer, asparagine is a dependency. The finding goes back to 1953, when serum from guinea pigs, but not from horses or rabbits, made transplanted lymphomas regress in mice ¹¹; the active agent was asparaginase, now made from Escherichia coli and Erwinia chrysanthemi ³. In a mouse model of breast cancer, cutting asparagine by asparaginase, by knocking down its synthetase or by diet reduced metastasis without slowing the primary tumour ¹².

In three sentences each

The sugar anchor

Oligosaccharyltransferase transfers a pre-assembled sugar block onto asparagines in the sequence Asn-X-Ser/Thr, where X is anything but proline; this N-glycosylation is essential in all eukaryotes ².

Starving leukaemia

Asparaginase hydrolyses blood asparagine to aspartate and ammonia; lymphoblasts that cannot make enough of their own die, and those that switch on asparagine synthetase resist the drug ^1,3.

Acrylamide in the Maillard reaction

Heated with reducing sugars, asparagine’s backbone breaks down to acrylamide; asparagine is a major amino acid in potatoes and cereals, which is why their fried and baked products carry the most ^6,7.

How it is made, moved and broken down

Asparaginase splits asparagine into aspartate and ammonia ³. Leukaemia cells that resist the drug turn on asparagine synthetase and a wider amino acid stress response driven by the transcription factor ATF4 ^1,13.

Carbon skeleton · glucogenicAsparaginase turns it into aspartate, which becomes oxaloacetate ^3,14.

Made and destroyedSynthetase builds it; asparaginase is the drug that undoes it ^1,3.

Aspartate + glutamine
Asparagine synthetaseASNS · ATP
Asparagine + glutamate
AsparaginaseASPG (drug: bacterial)
Aspartate + NH₃

N-glycosylationIn the endoplasmic reticulum ².

Asn in Asn-X-Ser/Thr + lipid-linked sugar
OligosaccharyltransferaseSTT3A, STT3B
N-glycoprotein

In the fryerWith reducing sugars at high temperature ^6,7.

Asparagine + glucose
The Maillard reactionheat
Acrylamide

Where it matters most

Brain: Depends on making its own asparagine ⁵.
Leukaemic lymphoblasts: Depend on asparagine from blood, the basis of asparaginase therapy ³.
Every secretory cell: N-glycosylation of asparagines in the endoplasmic reticulum ².

When it goes wrong

Inherited

Asparagine synthetase deficiency

ASNS · autosomal recessive

Congenital microcephaly, intellectual disability, progressive cerebral atrophy and intractable seizures, described in four families in 2013 ⁵; by 2017, 15 mutations had been linked to it ¹.

How it is foundExome sequencing; plasma asparagine may be low but is not always ⁵.

Drug

Asparaginase in acute lymphoblastic leukaemia

A core drug of treatment, with survival in childhood ALL now above 90% ¹⁵. Its toxicities are allergy and silent inactivation by antibodies ⁴, pancreatitis, which among 465 children with it needed mechanical ventilation in 8% ¹⁵, and thrombosis, in 5.2% of 1,752 children across 17 studies ¹⁶.

How it is foundNadir serum asparaginase activity ⁴.

Drug

Switching asparaginase after allergy

Erwinia asparaginase is antigenically distinct from the E. coli forms. Intravenous Erwinia reached adequate activity in 83% of patients 48 hours after a dose ¹⁷, and a recombinant Erwinia product reached it in 90 to 96% ¹⁸.

How it is foundNadir serum asparaginase activity ¹⁸.

Association

Dietary acrylamide

Acrylamide forms in fried and oven-cooked foods from asparagine and sugars ⁶. It is classified as probably carcinogenic to humans; asparaginase pre-treatment of potato reduced it by more than 80% ^6,19.

How it is measured

During asparaginase treatment, what is measured is the drug’s activity in serum, because asparagine itself keeps being destroyed after the blood is drawn ^4,20. Recombinant Erwinia asparaginase given three times a week kept nadir activity above 0.1 IU/mL in 90 to 96% of patients in its pivotal trial ¹⁸.

Serum asparaginase activityThe standard way to check that asparaginase is working, as a nadir level before the next dose ⁴.A nadir of at least 0.1 IU/mL is the accepted target; it detects silent inactivation, where antibodies neutralise the drug without an allergic reaction ^4,18.It measures the enzyme, not the asparagine it removes.
Plasma asparagine during asparaginaseDirectly shows depletion ²⁰.The drug keeps destroying asparagine in the tube; even immediate cooling does not stop it, so samples need an enzyme inhibitor or the result will be falsely low ²⁰.

Food, supplements and the evidence

Establishedreplicated in people, for a named outcome

Asparaginase is a core drug in childhood acute lymphoblastic leukaemia ^3,4.
Asparaginase treatment of food cuts acrylamide formation ¹⁹.

Uncertainsmall, short, mixed, surrogate or preclinical

Dietary asparagine restriction to limit cancer spread: shown in a mouse model of breast cancer, not in people ¹².

Sold asthe claim on the label, against the evidence

Nothing in this column.

What is strange about it

The leukaemia drug was found by accident, in guinea pig blood: in 1953 normal guinea pig serum made mouse lymphomas regress, and horse and rabbit serum did not ¹¹.

Food makers now treat raw potatoes and dough with asparaginase, the leukaemia drug’s enzyme, which cut acrylamide in chips and baked goods by more than 80% ¹⁹.

Asparagine is named after asparagus, but the smell asparagus gives to urine is sulfurous, and both producing and smelling it vary between people; not being able to smell it goes with a variant in a cluster of olfactory receptor genes ²¹.

Where it connects

In the Atlas

AspAspartateNegatively charged GlnGlutaminePolar, uncharged GluGlutamateNegatively charged ThrThreoninePolar, uncharged SerSerinePolar, uncharged

Topics on the map

On the map

A star in The rest of the amino acids, one of 6. Leukaemia cells cannot make it, so a bacterial enzyme that destroys it in the blood is a core leukaemia drug. Named after asparagus, where it was first found.

Find it on the map

Sources

21 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.

1
Lomelino CL, Andring JT, McKenna R, et al. Asparagine synthetase: function, structure, and role in disease.J Biol Chem · 2017 · 292(49):19952–19958doi:10.1074/jbc.R117.819060 · PMID 29084849
Review; stress-induced expression; asparaginase resistance; 15 mutations.
2
Kohda D. Structural basis of protein Asn-glycosylation by oligosaccharyltransferases.Adv Exp Med Biol · 2018 · 1104:171–199doi:10.1007/978-981-13-2158-0_9 · PMID 30484249
N-glycosylation at Asn-X-Ser/Thr.
3
Thakur M, Tiwari SK, Bansal S. L-asparaginase: a review of microbial production and protein engineering with translational applications for oncology and food safety.World J Microbiol Biotechnol · 2025 · 41(10):389doi:10.1007/s11274-025-04614-1 · PMID 41099876
Review; E. coli and Erwinia formulations; acrylamide use.
4
van der Sluis IM, Vrooman LM, Pieters R, et al. Consensus expert recommendations for identification and management of asparaginase hypersensitivity and silent inactivation.Haematologica · 2016 · 101(3):279–285doi:10.3324/haematol.2015.137380 · PMID 26928249
Activity monitoring and switching preparations.
5
Ruzzo EK, Capo-Chichi JM, Ben-Zeev B, et al. Deficiency of asparagine synthetase causes congenital microcephaly and a progressive form of encephalopathy.Neuron · 2013 · 80(2):429–441doi:10.1016/j.neuron.2013.08.013 · PMID 24139043
Four families; brain-specific dependence.
6
Mottram DS, Wedzicha BL, Dodson AT. Acrylamide is formed in the Maillard reaction.Nature · 2002 · 419(6906):448–449doi:10.1038/419448a · PMID 12368844
Asparagine as the crucial participant.
7
Stadler RH, Blank I, Varga N, et al. Acrylamide from Maillard reaction products.Nature · 2002 · 419(6906):449–450doi:10.1038/419449a · PMID 12368845
Released from asparagine with reducing sugars.
8
Robinson NE, Robinson AB. Molecular clocks.Proc Natl Acad Sci U S A · 2001 · 98(3):944–949doi:10.1073/pnas.98.3.944 · PMID 11158575
Deamidation rates of 306 asparagine sequences.
9
Kim E, Lowenson JD, MacLaren DC, et al. Deficiency of a protein-repair enzyme results in the accumulation of altered proteins, retardation of growth, and fatal seizures in mice.Proc Natl Acad Sci U S A · 1997 · 94(12):6132–6137doi:10.1073/pnas.94.12.6132 · PMID 9177182
Mice without the repair enzyme.
10
Luo W, Xu J, Chen H, et al. Synthesis of L-asparagine catalyzed by a novel asparagine synthase coupled with an ATP regeneration system.Front Bioeng Biotechnol · 2021 · 9:747404doi:10.3389/fbioe.2021.747404 · PMID 34631686
Extraction, chemical and enzymatic routes.
11
Kidd JG. Regression of transplanted lymphomas induced in vivo by means of normal guinea pig serum. I. Course of transplanted cancers of various kinds in mice and rats given guinea pig serum, horse serum, or rabbit serum.J Exp Med · 1953 · 98(6):565–582doi:10.1084/jem.98.6.565 · PMID 13109110
The original observation.
12
Knott SRV, Wagenblast E, Khan S, et al. Asparagine bioavailability governs metastasis in a model of breast cancer.Nature · 2018 · 554(7692):378–381doi:10.1038/nature25465 · PMID 29414946
Mouse model.
13
Ferguson DC, McCorkle JR, Barnett KR, et al. Amino acid stress response genes promote L-asparaginase resistance in pediatric acute lymphoblastic leukemia.Blood Adv · 2022 · 6(11):3386–3397doi:10.1182/bloodadvances.2022006965 · PMID 35671062
ATF4 targets in resistance.
14
Borst P. The malate-aspartate shuttle (Borst cycle): how it started and developed into a major metabolic pathway.IUBMB Life · 2020 · 72(11):2241–2259doi:10.1002/iub.2367 · PMID 32916028
Aspartate and oxaloacetate.
15
Wolthers BO, Frandsen TL, Baruchel A, et al. Asparaginase-associated pancreatitis in childhood acute lymphoblastic leukaemia: an observational Ponte di Legno Toxicity Working Group study.Lancet Oncol · 2017 · 18(9):1238–1248doi:10.1016/S1470-2045(17)30424-2 · PMID 28736188
465 children with pancreatitis from 26 trials.
16
Caruso V, Iacoviello L, Di Castelnuovo A, et al. Thrombotic complications in childhood acute lymphoblastic leukemia: a meta-analysis of 17 prospective studies comprising 1752 pediatric patients.Blood · 2006 · 108(7):2216–2222doi:10.1182/blood-2006-04-015511 · PMID 16804111
Thrombosis in 5.2%.
17
Vrooman LM, Kirov II, Dreyer ZE, et al. Activity and toxicity of intravenous Erwinia asparaginase following allergy to E. coli-derived asparaginase in children and adolescents with acute lymphoblastic leukemia.Pediatr Blood Cancer · 2016 · 63(2):228–233doi:10.1002/pbc.25757 · PMID 26376459
30 patients.
18
Maese L, Loh ML, Choi MR, et al. Recombinant Erwinia asparaginase (JZP458) in acute lymphoblastic leukemia: results from the phase 2/3 AALL1931 study.Blood · 2023 · 141(7):704–712doi:10.1182/blood.2022016923 · PMID 36108304
167 patients; adequate activity in 90–96% in the chosen schedule. Manufacturer-sponsored.
19
Jana A, Biswas S, Ghosh R, et al. Recent advances in L-asparaginase enzyme production and formulation development for acrylamide reduction during food processing.Food Chem X · 2024 · 25:102055doi:10.1016/j.fochx.2024.102055 · PMID 39758072
More than 80% acrylamide reduction with enzyme pre-treatment.
20
Lanvers-Kaminsky C, Westhoff PS, D’Incalci M, et al. Immediate cooling does not prevent the ex vivo hydrolysis of L-asparagine by asparaginase.Ther Drug Monit · 2014 · 36(4):549–552doi:10.1097/FTD.0000000000000030 · PMID 24342897
Ex vivo destruction of asparagine in the tube.
21
Pelchat ML, Bykowski C, Duke FF, et al. Excretion and perception of a characteristic odor in urine after asparagus ingestion: a psychophysical and genetic study.Chem Senses · 2011 · 36(1):9–17doi:10.1093/chemse/bjq081 · PMID 20876394
Individual differences in producing and smelling the odour.

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