In their catalytic center, hydrogenases manufacture molecular hydrogen (H2) from two protons and two electrons. They extract the protons required for this process from the surrounding water and transfer them – via a transport chain – into their catalytic core. The exact proton pathway through the hydrogenase had as yet not been understood. “This transfer pathway is a jigsaw piece, crucial for understanding the interplay of cofactor and protein which is the reason why biocatalysts are so much more efficient than hydrogen-producing chemical complexes,” explains Dr. Martin Winkler, one of the authors of this study from the Photobiotechnology research group at RUB.