Evidence of enzymatic catalysis of oxygen reduction on stainless steels under marine biofilm

Cathodic current trends on stainless steel samples with different surface percentages covered by biofilm and potentiostatically polarized in natural seawater were studied under oxygen concentration changes, temperature increases, and additions of enzymic inhibitors to the solution. The results showed that on each surface fraction covered by biofilm the oxygen reduction kinetics resembled a reaction catalyzed by an immobilised enzyme with high oxygen affinity (apparent Michaelis-Menten dissociation constant close to KO2 M 10 mM) and low activation energy (W 20 KJ mole71). The proposed enzyme rapidly degraded when the temperature was increased above the ambient (half-life time of *1 day at 258C, and of a few minutes at 508C). Furthermore, when reversible enzymic inhibitors (eg sodium azide and cyanide) were added, the cathodic current induced by biofilm growth was inhibited.