The difference a Se makes?: Oxygen-tolerant hydrogen production by the [NiFeSe]-hydrogenase from Desulfomicrobium baculatum

Protein film voltammetry studies of the [NiFeSe]-hydrogenase from Desulfomicrobium baculatum show it to be a highly efficient H-2 cycling catalyst. In the presence of 100% H-2, the ratio of H-2 production to H-2 oxidation activity is higher than for any conventional [NiFe]-hydrogenases (lacking a selenocysteine ligand) that have been investigated to date. Although traces of O-2 (<< 1%) rapidly and completely remove H-2 oxidation activity, the enzyme sustains partial activity for H-2 production even in the presence of 1% O-2 in the atmosphere. That H-2 production should be partly allowed, whereas H-2 oxidation is not, is explained because the inactive product of O-2 attack is reductively reactivated very rapidly, but this requires a potential that is almost as negative as the thermodynamic potential for the 2H(+)/H-2 Couple. The study provides further encouragement and clues regarding the feasibility of microbial/enzymatic H-2 production free from restrictions of anaerobicity.