Metallothioneins (MT) are a group of Cys-rich amino acid proteins with low molecular weight (5-10 kDa) that through the groups of thiol cysteine amino acids, have a variety of functions, including heavy metals detoxcification, metal metabolism and free radical scavenging activity. Avicennia marina has a high ability to absorb and accumulate heavy metals. However there is little information about MT in this plant. In the present work, the gene encoding AmMT2 as an type 2 from Avicennia marina was synthesized and cloned in pET41a. After induction with IPTG the protein AmMT was heterologously expressed in Escherichia coli as carboxy-terminal extensions of glutathione-S-transferase (GST-AmMT2). The tolerance of bacteria expressing GST-AmMT2 to ZnSO4, CdCl2, CuSO4, NiCl2 and FeSO 4 was compered to control by plotting their growth curve. In addition, the amount of metals that was removed from medium was determined using atomic absorption spectroscopy (AAS). The results show that the strain R-AmMT2 is able to remove Zinc, copper, cadmium, iron and nickel from media. In addition we found that the strain R-AmMT2 had higher tolerance to hydrogen peroxide than control strain. In agreement with this result, the assay of catalase activity in R-AmMT2 was higher than that from control strain. A significant amount of pure protein GST-AmMT2 was producted using affinity chromatography and gel filtration. The form of apoprotein was produced using acidic pH and removal of metals whit gel filtration. Then apo form was exposed to saturated amounts of zinc and iron The metal-protein was provided by pH-returning,Then removed free metals by gel filtration. However, catalase and ascorbate peroxidase activity increased by adding Fe/GST-AmMT2 to total protein extracted from E. coli bacteria and total protein extracted from mangroves, adding apo protein form did not have any effect on the activity of these enzymes.It seems that AmMT2 by exchanging iron metal increased activity these enzymes. Based on this results, AmMT2 not only plays a role in the detoxification of metals, but also provides metal for metalloenzymes whose activity is metal-dependent, which increased their activity. Increasing the activity of metalloenzymes such as ascorbate peroxidase and catalase leads to increased cellular tolerance to hydrogen peroxide. Key words : Metallothionin, Heavy metals, Tolerance, hydrogen peroxide.
