Substrate interaction at an iron-sulfur face of the FeMo-cofactor during nitrogenase catalysis.
Nitrogenase catalyzes biological dinitrogen fixation, the reduction of N(2) to 2NH(3). Recently, the binding site for a non-physiological alkyne substrate (propargyl alcohol, HC triple bond C-CH(2)OH) was localized to a specific Fe-S face of the FeMo-cofactor approached by the MoFe protein amino acid alpha-70(Val). Here we provide evidence to indicate that the smaller alkyne substrate acetylene (HC triple bond CH), the physiological substrate dinitrogen, and its semi-reduced form hydrazine (H(2)N-NH(2)) interact with the same Fe-S face of the FeMo-cofactor. Hydrazine is a relatively poor substrate for the wild-type (alpha-70(Val)) MoFe protein. Substitution of the alpha-70(Val) residue by an amino acid having a smaller side chain (alanine) dramatically enhanced hydrazine reduction activity. Conversely, substitution of alpha-70(Val) by an amino acid having a larger side chain (isoleucine) significantly lowered the capacity of the MoFe protein to reduce dinitrogen, hydrazine, or acetylene.
Department of Chemistry and Biochemistry, Utah State University, Logan, Utah 84322, USA.
Brett M
BM
Barney
Robert Y
RY
Igarashi
Patricia C
PC
Dos Santos
Dennis R
DR
Dean
Lance C
LC
Seefeldt
D000114:Acetylene / Q000737:chemistry; D000409:Alanine / Q000737:chemistry; D016948:Azotobacter vinelandii / Q000378:metabolism; D001665:Binding Sites; D002384:Catalysis; D004305:Dose-Response Relationship, Drug; D006834:Hydrazines / Q000737:chemistry / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D007501:Iron / Q000737:chemistry; D007532:Isoleucine / Q000737:chemistry; D007700:Kinetics; D046911:Macromolecular Substances; D008956:Models, Chemical; D008958:Models, Molecular; D008983:Molybdoferredoxin / Q000737:chemistry*; D009584:Nitrogen / Q000737:chemistry; D009591:Nitrogenase / Q000737:chemistry*; D010084:Oxidation-Reduction; D011485:Protein Binding; D013379:Substrate Specificity
D006834:Hydrazines; D046911:Macromolecular Substances; D008983:Molybdoferredoxin; D007532:Isoleucine; C029424:hydrazine; D007501:Iron; D009591:Nitrogenase; D009584:Nitrogen; D000114:Acetylene; D000409:Alanine