Phytochelatins
Phytochelatins are small polypeptide
compounds produced in plants by enzymes which are expressed in response
to heavy-metals (Cd2+, Pb4+) or oxyanions (SeO42-)(Salisbury and Ross,
1992). PCs are of the general form (yGlu-Cys)nGly with size ranging from
1.5 - 4 kDa. They are produced by a cleavage of a Gly unit off glutathione
(yGlu-Cys-Gly) by an enzyme called Phytochelatin synthase (yglutamyl-cysteine-dpt),
resulting in a (yGlu-Cys) fragment which is then combined to another
glutathione molecule to yield (yGlu-Cys)2Gly. The process can be repeated
several times to increase the number of (yGlu-Cys) units added to a glutathione
molecule. Phytochelatin synthase (PS) was recently cloned, and is available
for biotechnological manipulation (Vatamanuik, et al. 1999).
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