Nitrogenase fromthePhotosynthetic Bacterium Rhodopseudomonas capsulata: Purification andMolecular Properties

Nitrogenase proteins wereisolated fromcultures ofthephotosynthetic bacterium Rhodopseudomonas capsulata grownonalimiting amountofammonia. Underthese conditions, thenitrogenase N2aseA wasactive invivo, and nitrogenase activity invitro wasnotdependent uponmanganese andtheactivatingfactor. Thenitrogenase proteins werealsoisolated fromnitrogen-limited cultures inwhich theinvivo nitrogenase activity hadbeenstopped byanammonia shock. Thisnitrogenase activity, N2aseR,showed aninvitro requirement for manganese andtheactivating factor formaximal activity. TheMo-Feprotein (dinitrogenase) wascomposed oftwodissimilar subunits withmolecular weights of55,000 and59,500; theFeprotein (dinitrogenase reductase), fromeither typeof culture, wascomposed ofasingle subunit (molecular weight, 33,500). Themetal andacid labile sulfur contents ofbothnitrogenase proteins weresimilar tothose found forpreviously isolated nitrogenases. TheFeproteins frombothN2ase A andN2ase Rcontained phosphate andribose, 2molofeachpermolofN2ase RFe protein andabout 1molofeachpermolofN2aseA Feprotein. Thegreatest difference between thetwotypes ofFeprotein wasthat theN2ase R Feprotein contained about 1molpermolofanadenine-like molecule, whereas theN2ase A Feprotein content ofthis compound wasinsignificant. Theseresults arecompared withvarious models previously presented fortheshort-term regulation of nitrogenase activity inthephotosynthetic bacteria.