The active sites of molybdenum- and tungsten-containing enzymes

Protein X-ray crystallography has revealed the structures of the active sites of several molybdenum- and tungsten-containing enzymes that catalyze formal hydroxylation and oxygen atom transfer reactions. Each molybdenum (or tungsten) atom is coordinated by one (or two) ene-dithiolate groups of a novel pterin (molybdopterin), and the active sites are further differentiated from one another by the number of terminal oxo and/or sulfido groups and by coordinated amino acid residues. These active-site structures have no precedent in the coordination chemistry of molybdenum and tungsten.