Canavanine

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Canavanine
Chemical structure of L-(+)-(S)-canavanine
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 Edit this at Wikidata
EC Number
  • 624-714-2
KEGG
MeSH Canavanine
UNII
  • InChI=1S/C5H12N4O3/c6-3(4(10)11)1-2-12-9-5(7)8/h3H,1-2,6H2,(H,10,11)(H4,7,8,9)/t3-/m0/s1
  • N[C@@H](CCON=C(N)N)C(O)=O
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 in alcohol, ether, benzene
log P -0.91 (predicted)
Vapor pressure 1.61 μPa (predicted)
Acidity (pKa) 2.35 (carboxylic acid), 7.01 (oxoguanidinium), 9.22 (ammonium)
Hazards
GHS labelling:
GHS07: Exclamation mark
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 their standard state (at 25 °C [77 °F], 100 kPa).

L-(+)-(S)-Canavanine is a

herbivores (due to cells mistaking it for arginine) and a vital source of nitrogen for the growing embryo.[citation needed] The related L-canaline is similar to ornithine
.

Toxicity

The mechanism of canavanine's toxicity is that organisms that consume it typically mistakenly incorporate it into their own proteins in place of L-arginine, thereby producing structurally aberrant proteins that may not function properly. Cleavage by arginase also produces canaline, a potent insecticide.

The toxicity of canavanine may be enhanced under conditions of protein starvation,

movie) Into the Wild
).

Side-by-side comparison of the structures of canavanine and arginine, with the difference highlighted
Chemical structure of canavanine compared to arginine

In mammals

NZB/W F1, NZB, and DBA/2 mice fed L-canavanine develop a syndrome similar to

systemic lupus erythematosus,[1] while BALB/c mice fed a steady diet of protein containing 1% canavanine showed no change in lifespan.[3]

primates, including humans, and other auto-immune diseases. Often stopping consumption reverses the problem.[4][5][6]

Tolerance

Some specialized herbivores tolerate L-canavanine either because they metabolize it efficiently (cf. L-canaline) or avoid its incorporation into their own nascent proteins.

By metabolic detoxification

Herbivores may be able to metabolize canavanine efficiently. The beetle Caryedes 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]

By selectivity

An example of this ability can be found in the larvae of the tobacco budworm

lethal concentration 50 or LC50 300 mM) amounts of dietary canavanine.[8] These larvae fastidiously avoid incorporation of L-canavanine into their nascent proteins due to gastrointestinal expression of canavanine hydrolase, an enzyme that cleaves L-canavanine into L-homoserine and hydroxyguanidine, and L-arginine kinase, which phosphorylates L-canavanine.[9] In contrast, larvae of the tobacco hornworm Manduca 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 radiolabeled L-arginine and L-canavanine have shown that in Manduca sexta, the ratio of incorporation is about 3 to 1.[10]

megacarpa seeds contain high levels of canavanine. The beetle Caryedes 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 radiolabeled L-canavanine incorporated into newly synthesized proteins is barely measurable. Moreover, this beetle uses canavanine as a nitrogen source (see above).[11]

See also

References

  1. ^
    PMID 16890899
    .
  2. doi:10.1016/j.wem.2014.08.014
  3. PMID 15733319
    .
  4. PMID 1862241
    .
  5. PMID 8092103.[unreliable medical source?
    ]
  6. ^ http://vegpeace.org/rawfoodtoxins.html[full citation needed][permanent dead link][unreliable medical source?]
  7. doi:10.1126/science.202.4367.528
    .
  8. doi:10.1016/0048-3575(86)90005-2
    .
  9. PMID 9122181
    .
  10. PMID 3455753
    .
  11. S2CID 26741233
    .

Bibliography

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