Phytochelatins, enzyme synthesis

In contrast to MT induction, the available evidence suggests that PC synthesis is not stimulated by direct transcriptional activation. PCs can be synthesised very rapidly (within 5 min) in response to metals entering the cells, even when protein synthesis is totally inhibited (Scheller et al., 1987 Robinson etal., 1988). Phytochelatin synthase thus appears to be a constitutive enzyme. Loeffler et al. (1989) have shown that, for the enzyme purified from Silene cucubalus, metal ion induction is a post-... 

As an indirect effect of increased metal uptake, the physiological state of the cell can alter and defence mechanisms can be induced. Phytochelatin (metal binding proteins) synthesis and induction of free radical quenching enzymes and metabolites were frequently observed. Especially the latter can protect membranes against oxidative breakdown. 

The phytochelatins are compounds which have a structure based on glutathione, the structure of which can be regarded as (y-glutamylcysteine) -GSH. It is possible that enzymes with characteristics like the y-glutamyltranspeptidase described by Steinkamp and Rennenberg (1985) which use GSH as an amino-acyl acceptor could be involved in the synthesis of photochelatins. Evidence that phytochelatins are produced in response to the addition of heavy metals such as cadmium is discussed in Section IV,B and is reviewed by Rennenberg (1987). 

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