Barney Brett M, Igarashi Robert Y, Dos Santos Patricia C, Dean Dennis R, Seefeldt Lance C
Department of Chemistry and Biochemistry, Utah State University, Logan, Utah 84322, USA.
J Biol Chem. 2004 Dec 17;279(51):53621-4. doi: 10.1074/jbc.M410247200. Epub 2004 Oct 1.
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.
固氮酶催化生物固氮作用，即将N₂还原为2NH₃。最近，一种非生理性炔烃底物（丙炔醇，HC≡C-CH₂OH）的结合位点被定位到铁钼辅因子特定的铁硫面上，该铁硫面靠近钼铁蛋白氨基酸α-70（缬氨酸）。在此，我们提供证据表明，较小的炔烃底物乙炔（HC≡CH）、生理性底物氮气及其半还原形式肼（H₂N-NH₂）与铁钼辅因子的同一铁硫面相互作用。肼是野生型（α-70（缬氨酸））钼铁蛋白相对较差的底物。用侧链较小的氨基酸（丙氨酸）取代α-70（缬氨酸）残基可显著增强肼还原活性。相反，用侧链较大的氨基酸（异亮氨酸）取代α-70（缬氨酸）会显著降低钼铁蛋白还原氮气、肼或乙炔的能力。
