Copper phytochelatins of Mimulus guttatus

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Abstract
A copper-containing peptide has been isolated from the roots of copper-tolerant Mimulus guttatus after growth in copper. The behaviour of the peptide during gel filtration and ion-exchange chromatography was monitored by estimating copper. The peptide contained 39.1% glutamic acid/glutamine, 39.1% cysteine and 13.4% glycine which suggests that this copper-binding peptide is a phytochelatin with a ratio of Glx:Cys:Gly of 3:3:1. Its apparent molecular mass, estimated under dissociating conditions, was approximately 1600 Da. A second copper-containing peptide, which was not purified to such an extent, contained 29.7% glutamic acid/glutamine, 29.7% cysteine and 16.2% glycine; this peptide may also be a phytochelatin with a ratio of Glx:Cys:Gly of 2:2:1. Buthionine sulphoximine, a potent inhibitor of .gamma.-glutamyl-cysteinyl synthetase, caused only a small reduction in the growth of roots of copper-tolerant Mimulus guttatus in the absence of copper in the culture medium, but on exposure to both copper and buthionine sulphoximine root growth was greatly reduced. These results suggest that phytochelatin is involved in copper-tolerance in Mimulus guttatus.