The nitrogenase enzyme complex consists of two main protein components: the reductase and the nitrogenase. The reductase, also known as the Fe protein due to its iron-sulfur cluster, transfers electrons from a donor protein (such as ferredoxin) to the nitrogenase. The nitrogenase component, known as the MoFe protein because it contains both an iron-sulfur cluster and an iron-sulfur-molybdenum cluster, is responsible for splitting and reducing atmospheric nitrogen. For electron transfer to occur, these two complexes must temporarily associate. This association is driven by the hydrolysis of ATP, which induces a conformational change that brings the two halves together, allowing electrons to be passed from the reductase to the nitrogenase.