Purification and properties of a glutathione peroxidase from Southern bluefin tuna (Thunnus maccoyii) liver.

Comp Biochem Physiol B Biochem Mol Biol

School of Biological Sciences, Flinders University and Aquafin CRC, GPO Box 2100, Adelaide, South Australia 5001, Australia.

Published: May 2006

A glutathione peroxidase (GPX) protein was purified approximately 1000-fold from Southern bluefin tuna (Thunnus maccoyii) liver to a final specific activity of 256 micromol NADPH oxidised min(-1) mg(-1) protein. Gel filtration chromatography and denaturing protein gel electrophoresis of the purified preparation indicated that the protein has a native molecular mass of 85 kDa and is most likely a homotetramer with subunits of approximately 24 kDa. The Km values of the purified enzyme for hydrogen peroxide, cumene hydroperoxide, t-butyl hydroperoxide and glutathione were 12, 90, 90 and 5900 microM, respectively. The Km values for cumene hydroperoxide and t-butyl hydroperoxide were approximately 8-fold greater than the Km value for hydrogen peroxide. Thus, the SBT liver GPX has a considerably greater affinity for hydrogen peroxide than for the other two substrates. The pH optimum of the purified enzyme was pH 8.0. Immunoblotting experiments with polyclonal antibodies, raised against a recombinant human GPX, provided further evidence that the purified SBT enzyme is a genuine GPX.

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http://dx.doi.org/10.1016/j.cbpb.2006.01.011DOI Listing

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