 | |
| Names | |
|---|---|
| Preferred IUPAC name Canavanine | |
| Systematic IUPAC name (2S)-2-amino-4-{[(diaminomethylidene)amino]oxy}butanoic acid | |
| Identifiers | |
| |
3D model (JSmol) | |
| ChEBI | |
| ChemSpider | |
| DrugBank | |
| ECHA InfoCard | 100.153.281 |
| EC Number |
|
| KEGG | |
| MeSH | Canavanine |
| UNII | |
| |
| |
| Properties | |
| C5H12N4O3 | |
| Molar mass | 176.176 g·mol−1 |
| Density | 1.61 g·cm−3 (predicted) |
| Melting point | 184 °C (363 °F; 457 K) |
| Boiling point | 366 °C (691 °F; 639 K) |
| soluble | |
| Solubility | insoluble inalcohol,ether,benzene |
| logP | -0.91 (predicted) |
| Vapor pressure | 1.61 μPa (predicted) |
| Acidity (pKa) | 2.35 (carboxylic acid), 7.01 (oxoguanidinium), 9.22 (ammonium) |
| Hazards | |
| GHS labelling: | |
 | |
| Warning | |
| H302,H312,H332 | |
| Flash point | 214.6 °C (418.3 °F; 487.8 K) (predicted) |
Except where otherwise noted, data are given for materials in theirstandard state (at 25 °C [77 °F], 100 kPa). | |
L-(+)-(S)-Canavanine is anon-proteinogenic amino acid found in certainleguminous plants. It is structurally related to theproteinogenic α-amino acidL-arginine, the sole difference being the replacement of amethylene bridge (-CH
2- unit) in arginine with an oxa group (i.e., anoxygen atom) in canavanine. Canavanine is accumulated primarily in theseeds of the organisms which produce it, where it serves both as a highly deleterious defensive compound againstherbivores (due to cells mistaking it for arginine) and a vital source ofnitrogen for the growing embryo.[citation needed] The relatedL-canaline is similar toornithine.
The mechanism of canavanine's toxicity is that organisms that consume it typically mistakenly incorporate it into their ownproteins in place ofL-arginine, thereby producing structurally aberrant proteins that may not function properly. Cleavage byarginase also producescanaline, a potent insecticide.
The toxicity of canavanine may be enhanced under conditions of protein starvation,[1] and canavanine toxicity, resulting from consumption ofHedysarum alpinum seeds with a concentration of 1.2% canavanine weight/weight, has been implicated in the death of a malnourishedChristopher McCandless.[2] (McCandless was the subject ofJon Krakauer's book (and subsequentmovie)Into the Wild).
NZB/W F1, NZB, and DBA/2 mice fed L-canavanine develop a syndrome similar tosystemic lupus erythematosus,[1] while BALB/c mice fed a steady diet of protein containing 1% canavanine showed no change in lifespan.[3]
Alfalfa seeds and sprouts containL-canavanine. TheL-canavanine in alfalfa has been linked to lupus-like symptoms inprimates, including humans, and other auto-immune diseases. Often stopping consumption reverses the problem.[4][5][6]
Some specialized herbivores tolerateL-canavanine either because they metabolize it efficiently (cf.L-canaline) or avoid its incorporation into their own nascent proteins.
Herbivores may be able to metabolize canavanine efficiently. The beetleCaryedes brasiliensis is able to break canavanine down to canaline, then further detoxifies canaline by reductive deamination to form homoserine and ammonia. As a result, the beetle not only tolerates the chemical, but uses it as a source of nitrogen to synthesize its other amino acids to allow it to develop.[7]
An example of this ability can be found in the larvae of the tobacco budwormHeliothis virescens, which can tolerate large (lethal concentration 50 or LC50 300 mM) amounts of dietary canavanine.[8] These larvae fastidiously avoid incorporation ofL-canavanine into their nascent proteins due to gastrointestinal expression of canavanine hydrolase, an enzyme that cleavesL-canavanine intoL-homoserine and hydroxyguanidine, andL-arginine kinase, which phosphorylatesL-canavanine.[9] In contrast, larvae of the tobacco hornwormManduca sexta can only tolerate tiny amounts (1.0 microgram per kilogram of fresh body weight) of dietary canavanine because their arginine-tRNA ligase has little, if any, discriminatory capacity. No one has examined experimentally the arginine-tRNA synthetase of these organisms. But comparative studies of the incorporation of radiolabeledL-arginine andL-canavanine have shown that inManduca sexta, the ratio of incorporation is about 3 to 1.[10]
Diocleamegacarpa seeds contain high levels of canavanine. The beetleCaryedes brasiliensis is able to tolerate this however as it has the most highly discriminatory arginine-tRNA ligase known (as of 1982). In this insect, the level of radiolabeledL-canavanine incorporated into newly synthesized proteins is barely measurable. Moreover, this beetle uses canavanine as a nitrogen source (see above).[11]
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