Identification of the Elusive Hydronium Ion Exchanging Roles with a Proton in an Enzyme at Lower pH Values

Visible to neutrons: Although thought to be involved in biological processes, hydronium ions had never been identified in biomacromolecular crystallographic structures. A hydronium ion has now been found by neutron and X-ray crystallography to interchange with metal cofactors in the active site of an enzyme. Under more acidic conditions, the hydronium ion is dehydrated to a proton, and the binding site collapses (see picture).