title: Regulation of phytochelatin synthesis by zinc and cadmium in marine green alga, Dunaliella tertiolecta.
abstract: Although Cd(2+) is a more effective inducer of phytochelatin (PC) synthesis than Zn(2+) in higher plants, we have observed greater induction of PC synthesis by Zn(2+) than Cd(2+) in the marine green alga, Dunaliella tertiolecta. To elucidate this unique regulation of PC synthesis by Zn(2+), we investigated the effects of Zn(2+) and Cd(2+) on the activities of both phytochelatin synthase (PC synthase) and enzymes in the GSH biosynthetic pathway. PC synthase was more strongly activated by Cd(2+) than by Zn(2+), but the difference was not very big. On the other hand, gamma-glutamylcysteine synthetase (gamma-ECS) and glutathione synthetase (GS) were activated by both heavy metals, but their activities were higher in Zn-treated cells than in Cd-treated cells. Dose-dependent stimulation of intracellular reactive oxygen species (ROS) production was observed with Zn(2+), but not Cd(2+) treatment. These results suggest that Zn(2+) strongly promotes the synthesis of GSH through indirect activation of gamma-ECS and GS by stimulating ROS generation. This acceleration of the flux rate for GSH synthesis might mainly contribute to high level PC synthesis.
authors.affiliation: Environmental Bioengineering Laboratory, Graduate School of Pharmaceutical Sciences, Osaka University, Suita, Osaka 565-0871, Japan.
authors.forename: Naoki
authors.initials: N
authors.lastname: Tsuji
authors.forename: Nayumi
authors.initials: N
authors.lastname: Hirayanagi
authors.forename: Osamu
authors.initials: O
authors.lastname: Iwabe
authors.forename: Takashi
authors.initials: T
authors.lastname: Namba
authors.forename: Mariko
authors.initials: M
authors.lastname: Tagawa
authors.forename: Shiho
authors.initials: S
authors.lastname: Miyamoto
authors.forename: Hitoshi
authors.initials: H
authors.lastname: Miyasaka
authors.forename: Masahiro
authors.initials: M
authors.lastname: Takagi
authors.forename: Kazumasa
authors.initials: K
authors.lastname: Hirata
authors.forename: Kazuhisa
authors.initials: K
authors.lastname: Miyamoto
mesh_terms: D019881:Aminoacyltransferases / Q000378:metabolism*; D002104:Cadmium / Q000737:chemistry / Q000494:pharmacology*; D000460:Chlorophyta / Q000145:classification / Q000166:cytology / Q000187:drug effects / Q000201:enzymology*; D002851:Chromatography, High Pressure Liquid; D004305:Dose-Response Relationship, Drug; D004790:Enzyme Induction / Q000187:drug effects; D005434:Flow Cytometry / Q000379:methods; D005721:Glutamate-Cysteine Ligase / Q000378:metabolism; D005978:Glutathione / Q000096:biosynthesis; D005981:Glutathione Synthase / Q000378:metabolism; D008954:Models, Biological; D018384:Oxidative Stress / Q000187:drug effects; D017382:Reactive Oxygen Species / Q000378:metabolism; D013438:Sulfhydryl Compounds / Q000032:analysis; D015032:Zinc / Q000737:chemistry / Q000494:pharmacology*
chemical_list: D017382:Reactive Oxygen Species; D013438:Sulfhydryl Compounds; D002104:Cadmium; D019881:Aminoacyltransferases; C093784:glutathione gamma-glutamylcysteinyltransferase; D005721:Glutamate-Cysteine Ligase; D005981:Glutathione Synthase; D005978:Glutathione; D015032:Zinc