FeMoco
FeMoco, short for iron-molybdenum cofactor, is a complex metal cluster that is the active site of the nitrogenase enzyme. Nitrogenase is responsible for biological nitrogen fixation, the process by which atmospheric dinitrogen (N2) is converted into ammonia (NH3), a form of nitrogen usable by plants and other organisms. This process is essential for life as nitrogen is a key component of proteins, nucleic acids, and other vital biomolecules.
The FeMoco cofactor is buried deep within the nitrogenase protein, specifically in the MoFe protein subunit. Its structure is highly complex, consisting of a [MoFe7S9C] cluster. This cluster contains one molybdenum atom, seven iron atoms, nine sulfide ions, and one interstitial carbide atom located within the iron-sulfur cage.
The precise mechanism by which FeMoco catalyzes nitrogen fixation is still an active area of research. However, it is believed that the dinitrogen molecule binds to the FeMoco cluster, where it is then reduced by a series of electron and proton transfer steps. The electrons are delivered by the Fe protein component of the nitrogenase complex, and protons are derived from the surrounding aqueous environment. The Mo atom is thought to play a role in the initial binding of dinitrogen, and the iron atoms are crucial for electron transfer and the subsequent reduction of the bound N2.
The biosynthesis of FeMoco is a complex process involving multiple enzymes and chaperone proteins. The biosynthesis pathway is highly regulated, ensuring that the FeMoco cofactor is only synthesized under conditions of nitrogen limitation. Mutations in the genes involved in FeMoco biosynthesis can lead to nitrogen fixation deficiency and impaired plant growth.