The Catalytic Mechanisms of the Molybdenum and Tungsten Enzymes

Abstract

Molybdenum and tungsten are, respectively, the only second and third transition metal ions with well-defined functions in living organisms and with a single exception are found in association with a novel pyranopterin dithiolene cofactor called molybdopterin. This review focusses on the catalytic mechanisms of the molybdenum and tungsten enzymes, with an emphasis on the molybdenum and tungsten sites. Most, but not all, of the enzymes catalyze oxygen atom transferase redox chemistry, with the metal cycling between M(VI) and M(IV) formal oxidation states during the catalytic cycle. We discuss the range of reactions and what is known of mechanism for both oxo-transferase and non-oxo-transferase molybdenum and tungsten enzymes.