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.
Barney
Brett M
BM
Department of Chemistry and Biochemistry, Utah State University, Logan, Utah 84322, USA.
Igarashi
Robert Y
RY
Dos Santos
Patricia C
PC
Dean
Dennis R
DR
Seefeldt
Lance C
LC
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