Novel bacterial molybdenum and tungsten enzymes: three-dimensional structure, spectroscopy, and reaction mechanism.

The molybdenum enzymes 4-hydroxybenzoyl-CoA reductase and pyrogallol-phloroglucinol transhydroxylase and the tungsten enzyme acetylene hydratase catalyze reductive dehydroxylation reactions, i.e., transhydroxylation between phenolic residues and the addition of water to a triple bond. Such activities are unusual for this class of enzymes, which carry either a mononuclear Mo or W center. Crystallization and subsequent structural analysis by high-resolution X-ray crystallography has helped to resolve the reaction centers of these enzymes to a degree that allows us to understand the interaction of the enzyme and the respective substrate(s) in detail, and to develop a concept for the respective reaction mechanism, at least in two cases.