The Difference a Se Makes? Oxygen-Tolerant Hydrogen Production by the [NiFeSe]-Hydrogenase from Desulfomicrobium baculatum

Abstract

Protein film voltammetry studies of the [NiFeSe]-hydrogenase from Desulfomicrobium baculatum show it to be a highly efficient H₂ cycling catalyst. In the presence of 100% H₂, the ratio of H₂ production to H₂ oxidation activity is higher than for any conventional [NiFe]-hydrogenases (lacking a selenocysteine ligand) that have been investigated to date. Although traces of O₂ (≪ 1%) rapidly and completely remove H₂ oxidation activity, the enzyme sustains partial activity for H₂ production even in the presence of 1% O₂ in the atmosphere. That H₂ production should be partly allowed, whereas H₂ oxidation is not, is explained because the inactive product of O₂ attack is reductively reactivated very rapidly, but this requires a potential that is almost as negative as the thermodynamic potential for the 2H⁺/H₂ couple. The study provides further encouragement and clues regarding the feasibility of microbial/enzymatic H₂ production free from restrictions of anaerobicity.