Nitrogenase_MoFe_alpha_II: Nitrogenase MoFe protein, beta subunit. A group of proteins similar to the alpha subunit of the MoFe protein of the molybdenum (Mo-) nitrogenase. The nitrogenase enzyme catalyzes the ATP-dependent reduction of dinitrogen to ammonia. The Mo-nitrogenase is the most widespread and best characterized of these systems. Mo-nitrogenase consists of the MoFe protein (component 1) and the Fe protein (component 2). MoFe is an alpha2beta2 tetramer. Each alphabeta pair of MoFe contains one P-cluster (at the alphabeta interface) and, one molecule of iron molybdenum cofactor (FeMoco) contained within the alpha subunit. The Fe protein contains a single [4Fe-4S] cluster. Electrons are transferred from the [4Fe-4S] cluster of the Fe protein to the P-cluster of the MoFe and in turn to FeMoCo, the site of substrate reduction.