OXIDOREDUCTASE, NITROGEN FIXATION, MOFE PROTEIN, NITROGENASE, ISOLEUCINE, PROTON REDUCTION, NITROGEN, ACETYLENE, HYDRIDE REDUCTION, ATP-BINDING, IRON, IRON-SULFUR, METAL-BINDING, NUCLEOTIDE- BINDING, MOLYBDENUM INSIGHTS INTO SUBSTRATE BINDING AT FEMO-COFACTOR IN NITROGENASE FROM THE STRUCTURE OF AN ALPHA-70ILE MOFE PROTEIN VARIANT 3K1A