SACCORHIZA-POLYSCHIDES (PHAEOPHYCEAE, PHYLLARIACEAE) A NEW SOURCE FORVANADIUM-DEPENDENT HALOPEROXIDASES

Vanadium-dependent iodoperoxidases from the brown seaweed Saccorhiza p olyschides (Lightfoot) Batters, collected at three different locations along the Portuguese west coast, were extracted, purified and charact erized. Several extraction procedures were tested, including two-phase aqueous systems. The purification of the iodoperoxidases was achieved using hydrophobic interaction chromatography followed by chromatofocu sing. It was possible to isolate three different isoforms of the enzym e, which show mainly iodoperoxidase activity. The three native enzymes have a relative M-r around 125 kDa, and two subunits of M-r about 64 kDa. Reactivation studies of the apoenzymes with several metal ions re vealed that vanadium(V) was essential for enzymatic activity. These en zymes are remarkably thermostable, maintaining their maximum activity up to 50 degrees. The kinetic parameters for the enzyme catalysed iodo peroxidase reaction were obtained at pH 6.1. In the concentration rang e studied (0.2-8 mM) there was no inhibition by H2O2 whereas iodide in hibition was already apparent at the top values of the concentration r ange studied (2-25 mM). (C) 1998 Elsevier Science Ltd. All rights rese rved.