Phytochelatin

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Phytochelatins are oligomers of glutathione, produced by the enzyme phytochelatin synthase. They are found in plants, fungi, nematodes and all groups of algae including cyanobacteria. Phytochelatins act as chelators, and are important for heavy metal detoxification.^[1][2][3] They are abbreviated PC2 through PC11.

A mutant Arabidopsis thaliana lacking phytochelatin synthase is very sensitive to cadmium, but it grows just as well as the wild-type plant at normal concentrations of zink and copper, two essential metal ions, indicating that phytochelatin is only involved in resistance to metal poisoning.^[4]

Because phytochelatin synthase uses glutathione with a blocked thiol group in the synthesis of phytochelatin, the presence of heavy metal ions that bind to glutathione causes the enzyme to work faster. Therefore the amount of phytochelatin increases when the cell needs more phytochelatin to survive in an environment with high concentrations of metal ions.^[5]

Phytochelatin seems to be transported into the vacuole of plants, so that the metal ions it carries are stored safely away from the proteins of the cytosol.^[4]

Related peptides

There are groups of other peptides with a similar structure to phytochelatin, but where the last amino acid is not glycine:^[4][6]

History

Phytochelatin was first discovered in 1981 in fission yeast, and was named cadystin. It was then found in higher plants in 1985 and was named phytochelatin. In 1989 its enzyme, phytochelatin synthase, was discovered.^[6]

References

1. ^ Suk-Bong Ha, Aaron P. Smith, Ross Howden, Wendy M. Dietrich, Sarah Bugg, Matthew J. O'Connell, Peter B. Goldsbrough, and Christopher S. Cobbett , Phytochelatin Synthase Genes from Arabidopsis and the Yeast Schizosaccharomyces pombe, Plant Cell, Vol. 11, 1153-1164, June 1999
2. ^ Olena K. Vatamaniuk, Elizabeth A. Bucher, James T. Ward and Philip A. Rea, A new pathway for heavy metal detoxification in animals: phytochelatin synthase is required for cadmium tolerance in Caenorhabditis elegans, The Journal of Biological Chemistry, April 2001
3. ^ InterPro database page on phytochelatin synthase
4. ^ ^{a b c} Buchanan, Gruissem, Jones, Biochemistry & molecular biology of plants, 1st edition, American Society of Plant Physiology, 2000
5. ^ O K Vatamaniuk, S Mari, Y Lu, and P A Rea, Mechanism of Heavy Metal Ion Activation of Phytochelatin (PC) Synthase, J. Biol. Chem., Vol. 275, Issue 40, 31451-31459, October 6, 2000
6. ^ ^{a b} Masahiro Inouhe, Phytochelatins, Braz. J. Plant Physiol. vol.17 no.1 Londrina Jan./Mar. 2005