SDS-induced phenoloxidase activity of Helix aspersa maxima hemocyanin

Oxygen-transporting protein of the hemolimph of snails Helix aspersa maxima (HaH) was converted from being an oxygen carrier to a form which exhibited phenoloxidase activity by incubation with sodium dodecyl sulfate (SDS). On treatment with 1.73 mM SDS, for 3 min, significant increase of catalytic efficiency of hemocyanin towards substrate catechol (kcat/Km = 34.56 mM.min -1 versus kcat/Km = 0.093 mM.min -1 for native hemocyanin) was achieved. The highest o-diPO activity and enzyme efficiency of HaH (kcat/Km = 60.94 mM -1 min -1 ), after incubation in 1.73 mM SDS for 3 min, was determined towards substrate dopamine. Structural characterization by means of absorption and fluorescence spectroscopy and circular dichroism showed that SDS induced optimal conformational changes in the protein. As a result the active sites become more accessible to the molecules of the substrate and the hemocyanin can function as phenoloxidase.