Glutathione-mediated transfer of Cu(I) into phytochelatins.
Room temperature luminescence attributable to Cu(I)-thiolate clusters has been used to probe the transfer of Cu(I) from Cu(I)-glutathione complex to rabbit liver thionein-II and plant metal-binding peptides phytochelatins (gamma-Glu-Cys)2Gly, (gamma-Glu-Cys)3Gly and (gamma-Glu-Cys)4Gly. Reconstitutions were also performed using CuC1. The Cu(I)-binding stoichiometry of metallothionein or phytochelatins was generally independent of the Cu(I) donor. However, the luminescence of the reconstituted metallothionein or phytochelatins was higher when Cu(I)-GSH was the donor. This higher luminescence is presumably due to the stabilizing effect of GSH on Cu(I)-thiolate clusters. As expected, 12 Cu(I) ions were bound per molecule of metallothionein. The Cu(I) binding to phytochelatins depended on their chain length; the binding stoichiometries being 1.25, 2.0 and 2.5 for (gamma-Glu-Cys)2Gly, (gamma-Glu-Cys)3Gly and (gamma-Glu-Cys)4Gly respectively at neutral pH. A reduced stoichiometry for the longer phytochelatins was observed at alkaline pH. No GSH was found to associate with phytochelatins by a gel-filtration assay. The Cu(I) binding to (gamma-Glu-Cys)2Gly and (gamma-Glu-Cys)3Gly occurred in a biphasic manner in the sense that the relative luminescence increased approximately linearly with the amount of Cu(I) up to a certain molar ratio whereafter luminescence increased dramatically upon the binding of additional Cu(I). The luminescence intensity declined once the metal-binding sites were saturated. In analogy with the studies on metallothioneins, biphasic luminescence suggests the formation of two types of Cu(I) clusters in phytochelatins.
Mehra
R K
RK
Department of Entomology, University of California, Riverside 92521, USA.
Mulchandani
P
P
D000595:Amino Acid Sequence; D000818:Animals; D001692:Biological Transport; D002850:Chromatography, Gel; D003300:Copper / Q000378:metabolism*; D004355:Drug Stability; D005978:Glutathione / Q000494:pharmacology*; D008099:Liver / Q000378:metabolism; D008163:Luminescent Measurements; D008667:Metalloproteins / Q000378:metabolism*; D008668:Metallothionein / Q000378:metabolism; D008969:Molecular Sequence Data; D054811:Phytochelatins; D010940:Plant Proteins / Q000378:metabolism*; D011817:Rabbits; D013056:Spectrophotometry, Ultraviolet
D008667:Metalloproteins; D010940:Plant Proteins; D003300:Copper; D008668:Metallothionein; D054811:Phytochelatins; C028419:cuprous chloride; D005978:Glutathione