Nitrile hydratase is a quinoprotein. A possible new function of pyrroloquinoline quinone: activation of H2O in an enzymatic hydration reaction.

Nitrile hydratase has been proved to be a quinoprotein with pyrroloquinoline quinone (PQQ) as a prosthetic group. The broad shoulder from 300 to 500 nm in the absorption spectrum of Brevibacterium nitrile hydratase suggested the presence of PQQ. Since PQQ was attached to the enzyme through a covalent linkage, the chromophores were isolated by acid hydrolysis, protease digestion and successive chromatographic separation. The isolated chromophores showed the similar spectroscopic characteristics to those of obtained from the amine oxidase of Aspergillus niger, in which PQQ is covalently linked. The isolated chromophores potently activated apo-D-glucose dehydrogenase (EC 1.1.99.17), supporting the presence of PQQ or a PQQ-like compound in nitrile hydratase. The finding of PQQ in nitrile hydratase strongly suggests a new function of PQQ, i.e., the activation of H2O in the enzymatic hydration reaction.