S 2B or not 2B?

Abstract

In recent years a large collection of experimental information has prompted proposals that an atom, S2B, part of the catalytic metal cluster FeMo-co of the enzyme nitrogenase, is displaced during the enzyme mechanism in order to allow the binding of substrate N₂ to the adjacent Fe atoms. Computational investigation has generated a complete enzyme mechanism in which S2B is retained in its resting state position, and as such is an essential agent in the enzyme mechanism. A dilemma arises, between a disruptive mechanism – with S2B moved out of the way during the reaction steps – and a conservative mechanism – with S2B retained and necessarily used. Following the Prince of Denmark, is the 2B position of FeMo-co to be S or not to be S? I have assembled the evidence and arguments in this Perspective.