Enhancement of catalase and superoxide dismutase activities in transgenic Escherichia coli expressing rice metallothionein isoforms
Metallothioneins (MTs) are small, ubiquitous Cys-rich proteins known to be involved in the homeostasis of essential metals, detoxification of toxic metals and protection against oxidative stress. In the present work transgenic E.coli overexpressing different rice MT isoforms including OsMT1, OsMT2, OsMT3 and OsMT4 showed higher tolerance against hydrogen peroxide stress. Moreover the enzymatic activity of catalase (CAT) and superoxide dismutase (SOD) in the transgenic strains were higher than that in control strain when they were grown in the medium containing hydrogen peroxide. To understand the mechanistic action of MT on the removal of reactive oxygen species, the activity of CAT and SOD in the E.coli protein extract were assayed after addition of pure Zn2+/MTs, Fe2+/MT and apo/MT. whereas the activity of CAT and SOD did not change by addition of apo/MT, the activity of CAT and SOD were increased after addition of Fe2+/MTs and Zn2+/MTs, respectively. These results open new insights into the role of MT as activator of CAT and SOD by supplying metals.
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