Identification of a Key Catalytic Intermediate Demonstrates That Nitrogenase Is Activated by the Reversible Exchange of N2 for H2

摘要: Freeze-quenching nitrogenase during turnover with N2 traps an S = 1/2 intermediate that was shown by ENDOR and EPR spectroscopy to contain or a reduction product bound the active-site molybdenum–iron cofactor (FeMo-co). To identify this (termed here EG), we turned quench-cryoannealing relaxation protocol. The trapped state is allowed relax resting E0 in frozen medium at temperature below melting temperature; monitored periodically cooling sample cryogenic for analysis. During −50 °C cryoannealing of EG prepared under conditions which concentrations H2 ([H2], [N2]) are systematically independently varied, rate decay accelerated increasing [H2] slowed [N2] reaction mixture; correspondingly, accumulation greater low and/or high [N2]. influence these diatomics identifies as key catalytic formed b...