Studies on the Reconstitution of P-Cluster-Deficient Molybdenum-Iron Protein Diversity of Nitrogenase Systems in Diazotrophs Relationship Between nifZ and the Synthesis of P cluster in Nitrogenase MoFe Protein of Azotobacter vinelandii Purification and Properties of Nitrogenase MoFe Protein from a nif Z Deletion Strain of Azotobacter vinelandii