metallothionein -biomarker
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Zn>Cd &Hg>Cu
Pathiratne et al(2009) and Ghedtra et al (2010) Richard (1994) -MT induction -liver : Hg > Ag> Cu > Zn.
Metallothionein - a potential biomarker to assess the metal contamination in marine fishes-A review
MetalTranscription -of MT genes MT synthesis Cd can induce MT expression in Fishes. (Chen et al. 2005, Rovira et al. 2005, Choi et al. 2007) MT transcript proteins -bivalent metal - Zn, Cu, Pb, Fe, Co and Hg. ( Ikebuchi et al. 1986; Carginale et al. 1998; Riggio et al. 2003 ) Thiele in 1992- MT gene expression Metal concentration.4 MT genes-common promoter-several MREs- which binds to metal transcription factors-synthesis of MT.(Kling and Olsson in 1993).Factors Affecting the Metallothionein Estimations ageSexual maturity- max variation-femaleOlsson et al ( 1987) - Rainbow Trout hepatic MT levels
SexTissue type Route of exposure and experimental conditions Chowdhury et al (2005) -Rainbow trout -sub lethal concentration -waterborne Cd (0 or 3 g/L) or dietary Cd (0 or 500 mg/kg dry wt) -30 days Waterborne exposure group- highest MT- kidney - Gills liver. Dietary exposure group-kidney >> cecae and posterior intestine > liver and stomach > midintestine > gills. Exogenous and endogenous substancesExperimental problems with MTsOlsson 1996Metal Type Seasonal variationsFuture prospects1. Inorganic HgInvitro studiesCell cultureInvivo influence Not clear
Organic-mercury complex2. Standardization of methods 3.Different methodology used by researchers Thiele D J (1992).Metal Regulated Transscription in Eukaryotes. Nucleic Acid Research.210;1183-1188.Kling, P. & Olsson. P. E. (1993). Metal regulation of the rainbow trout metallothionein-A gene. In: proceedings of the Seventh International Symposium on Responses of Marine Organisms to Pollutants.Geroge S.G.,Hadgson P.A.,Tybler .P.,Tedd.K.,(1996).Inducability of Metallothionein mRNA expression and Cadmium tolerance in larva of teleosts the turbot (Scophthalmus maximus).Fundamental Application of Toxicology 33:91-99.Singh M R. (2007). Impurities-heavy metals: IR prespective.(George et al.,1996)Reference Vijaya * and R. Jayakumar** *Research Scholar, **Assistant Professor, Department of Environmental Science, GITAM University, Bengaluru Campus, Nagadenahalli-562 163. KARNATAKA. E-mail:[email protected]
MT as BiomarkerUbiquitous , stable & inducible proteins, Mw 6-8kDa, pI-8.3High cysteine content (20-30%) - 61 amino acids - no aromatic amino acids. Binds to metals - metal thiolate bonds.Metal homeostasis Zn ,Cu & detoxification Cd, Hg, Pt, Ag
Introduction Metallothionein (MTs)
Cd Higher affinity to MTs tan Zn Displace Zn from MT binding site(Hollis L.C and C.M.Wood, 2001)Maximum induction MTs in Tilapia 2mg/kg of CdNo further change (Y.F.Ueng et al. 1996)