Radical SAM-Dependent Carbon Insertion into the Nitrogenase M-Cluster

Abstract

A Radical Mechanism The bacterial enzyme nitrogenase plays a key role in the global nitrogen cycle by catalyzing the reduction of N 2 to ammonia. At the heart of the enzyme is a metal-sulfur cluster that contains an interstitial light atom recently identified as a carbide. The identification raised questions concerning the role of the carbide in the enzyme mechanism and how it is inserted into the metal cluster. Wiig et al. (p. 1672 ; see the Perspective by Boal and Rosenzweig ) now show that the carbide derives from S-adenosylmethionine (SAM) and is inserted into the core by the radical SAM enzyme NifB.