Hydrogens visualized in hydrogenase enzyme

[NiFe] hydrogenases use nickel and iron to catalyse the reversible oxidation of molecular hydrogen. They are the focus of much research worldwide because of their potential in biotechnology and in serving as natural models for biomimetic catalysts in the energy sector for hydrogen production and conversion. In protein X-ray crystallography it is notoriously difficult to detect hydrogens, a particularly significant problem in hydrogenases where hydrogens are involved directly in the reaction. Hideaki Ogata et al. have succeeded in obtaining a sub-ångström resolution X-ray crystal structure of [NiFe] hydrogenase leading to detection of most of the hydrogens even close to the metal ions. Using their technique authors were able to detect the products of the heterolytic splitting of dihydrogen: a hydride that bridges the Ni and Fe ions, and a proton that is attached to the sulfur of a cysteine ligand.