Phytochelatin

Phytochelatins (also Cadystin and metallothionein Class III) are polypeptides which are enzymatically formed in response to heavy metals in plants and fungi. They bind to heavy metals ( eg cadmium ) and detoxify it that way.

Just as glutathione, phytochelatins consist of the amino acids glutamic acid, cysteine ​​and glycine, here too the γ -carboxyl group (not the α -carboxyl group ) of glutamic acid with the amino group of the cysteine ​​residue is connected, as phytochelatins are enzymatically synthesized from glutathione. The enzyme phytochelatin synthase cleaves the glycine of a glutathione molecule, and adds another glutathione molecule. The simplest phytochelatin therefore has the structure γGlu -Cys -Cys -Gly - γGlu. This can be extended by adding one or more further γGlu -Cys. Most of the other polypeptides are encoded by a specific gene, however, and are synthesized in the translation.

Phytochelatins are formed in response to a wide range of heavy metals and other toxic metallic and semi-metallic elements and initiate a detoxification mechanism: They bind with the sulfhydryl groups of their cysteine ​​residues to the metal ions and are transported into the vacuole with them. In the vacuole, the heavy metals are shielded from the metabolism in the cytosol, so that they can not interfere with the enzymatic reactions of metabolism there. The formed phytochelatin - metal complexes can be purified by chromatography and partially characterize it.

Phytochelatins in 1985 about the same time discovered by two research groups, purified and characterized for the first time.