Cloning and characterization of two glutathione peroxidase cDNAs from southern bluefin tuna (Thunnus maccoyii).

Glutathione peroxidases (GPXs; EC 1.11.19) are key enzymes in the antioxidant defence systems of living organisms, including fish.

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

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.

Electrochemical characterization of purified Rhus vernicifera laccase: voltammetric evidence for a sequential four-electron transfer.

Rhus vernicifera (Rv) laccase was purified to electrophoretic homogeneity by hydrophobic interaction chromatography. A comprehensive study of the direct electrochemistry of Rv laccase covalently immobilized at a gold electrode using alkanethiol monolayers was undertaken. The observed midpoint potential was 410 mV versus the normal hydrogen electrode (NHE), consistent with reduction potentials obtained by potentiometric titration for the T1 copper site.