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Stimulation of peroxidation in rat liver microsomes by (copper, zinc)-metallothioneins
J R Arthur1, I Bremner, P C Morrice
1Rowett Research Institute, Bucksburn, Aberdeen, U.K.
Abstract:
The abilities of pig liver (copper, zinc) metallothionein I and rat liver zinc metallothionein II to modify lipid peroxidation in incubations of liver microsomes have been compared with the activities of reduced glutathione, mannitol, quinacrine, EDTA, dimethyl-pyrroline-N-oxide and phenyl-butyl-nitrone. Lipid peroxidation was determined by assay of thiobarbituric acid reactive substance formation in incubations of microsomes with iron/ADP or a mixture of xanthine and xanthine oxidase. Zinc metallothionein II had no effect on the extent of peroxidation in either system but (copper, zinc) metallothionein I caused a stimulation of peroxidation initiated by xanthine and xanthine oxidase, all other compounds tested were inhibitory. Gel exclusion chromatography of incubations of (copper, zinc) metallothionein I with xanthine and xanthine oxidase revealed aggregation of the metalloprotein. This may have exposed copper in a form capable of initiating peroxidation.
Insights
Pig liver (copper, zinc) metallothionein I stimulated lipid peroxidation, unlike other tested compounds. This metalloprotein may expose copper, initiating peroxidation, while rat liver zinc metallothionein II had no effect.
Area of Science:
- Biochemistry
- Toxicology
- Metalloprotein research
Background:
- Lipid peroxidation is a key indicator of oxidative stress in biological systems.
- Metallothioneins (MTs) are proteins involved in metal detoxification and antioxidant defense.
- Understanding MTs' role in oxidative processes is crucial for cellular health.
Purpose of the Study:
- To compare the effects of pig liver (copper, zinc) metallothionein I and rat liver zinc metallothionein II on lipid peroxidation.
- To evaluate the modulatory activities of these metallothioneins against common antioxidants and free radical scavengers.
- To investigate the mechanism by which metallothioneins influence lipid peroxidation.
Main Methods:
- Lipid peroxidation was quantified by measuring thiobarbituric acid reactive substance (TBARS) formation.
- Microsomal incubations were subjected to iron/ADP-induced or xanthine/xanthine oxidase-initiated peroxidation.
- Gel exclusion chromatography was used to analyze metalloprotein aggregation.
Main Results:
- Pig liver (copper, zinc) metallothionein I significantly stimulated lipid peroxidation initiated by xanthine/xanthine oxidase.
- Rat liver zinc metallothionein II exhibited no effect on lipid peroxidation in either experimental system.
- All other tested compounds, including reduced glutathione and scavengers, demonstrated inhibitory effects on lipid peroxidation.
Conclusions:
- Pig liver (copper, zinc) metallothionein I can promote lipid peroxidation, contrasting with the protective roles of other agents.
- Metalloprotein aggregation observed during incubation suggests exposed copper may initiate peroxidation.
- These findings highlight a potentially pro-oxidant role for specific metallothionein isoforms under certain conditions.