Canavanine

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Canavanine
Chemical structure of L-(+)-(S)-canavanine
Identifiers
CAS number 543-38-4 YesY
PubChem 275
ChemSpider 388342
DrugBank DB01833
KEGG C00308
MeSH Canavanine
ChEBI CHEBI:609827
Jmol-3D images Image 1
Properties
Molecular formula C5H12N4O3
Molar mass 176.17 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)
Solubility in water soluble
Solubility insoluble in alcohol, ether, benzene
log P -0.91 (predicted)
Vapor pressure 1.61 μPa (predicted)
Hazards
Flash point 214.6 °C (predicted)
Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
Infobox references

L-(+)-(S)-Canavanine is a non-proteinogenic α-amino acid found in certain leguminous plants. It is structurally related to the proteinogenic α-amino acid L-arginine, the sole difference being the replacement of a methylene bridge (-CH
2
- unit) in arginine with an oxa group (i.e., an oxygen atom) in canavanine. Canavanine is accumulated primarily in the seeds of the organisms which produce it, where it serves both as a highly deleterious defensive compound against herbivores and a vital source of nitrogen for the growing embryo[1] (see also L-canaline). 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.

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

Some specialized herbivores tolerate L-canavanine either because they metabolize it efficiently (cf. L-canaline) or avoid its incorporation into their own nascent proteins. An example of this ability can be found in the tobacco budworm Heliothis virescens the larvae of which can tolerate massive amounts of dietary canavanine. These larvae fastidiously avoid incorporation of L-canavanine into their nascent proteins (presumably by virtue of highly discriminatory Arginine—tRNA ligase, the enzyme responsible for the first step in the incorporation of arginine into proteins). In contrast, larvae of the tobacco hornworm Manduca sexta can only tolerate tiny amounts (1.0 microgram per kilogram of fresh body weight[2]) 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.

Dioclea 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. 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 to synthesize its other amino acids to allow it to develop.[3]

Alfalfa seeds and sprouts contains L-canavanine. The L-canavanine in alfalfa has been linked to lupus-like symptoms in primates, including humans, and other auto-immune diseases. Often stopping consumption reverses the problem.[4][5][6]

See also[edit]

References[edit]

  1. ^ "Non-protein amino acids (NPA)". January 2009. Archived from the original on 2011-01-22. Retrieved 2011-01-22. 
  2. ^ Rosenthal, G .A.; Dahlman, D. L. (1986-01-01). "L-Canavanine and protein synthesis in the tobacco hornworm Manduca sexta". Proc Natl Acad Sci U S A 83 (1): 14–18. doi:10.1073/pnas.83.1.14. PMC 322781. PMID 3455753. Retrieved 2011-01-22. 
  3. ^ Rosenthal, Gerald A.; Hughes, Charlie G.; Janzen, Daniel H. (1982-07-23). "L-Canavanine, a Dietary Nitrogen Source for the Seed Predator Caryedes brasiliensis (Bruchidae)". Science 217 (4557): 353–355. doi:10.1126/science.217.4557.353. PMID 17791516. Retrieved 2011-01-22. 
  4. ^ http://www.ncbi.nlm.nih.gov/pubmed/1862241
  5. ^ http://ajcn.nutrition.org/content/60/4/639.full.pdf
  6. ^ http://vegpeace.org/rawfoodtoxins.html

Bibliography[edit]