Catalytic reduction of acetylene in the presence of molybdenum and iron clusters, including FeMo cofactor of nitrogenase

Effect of the acidity and chemical nature of the protonating agent on the rate of acetylene reduction catalyzed by the nitrogenase active site isolated from the enzyme

“…Thus, the results of this study of the protonating agent acidity effect on the rate of acetylene reduction catalyzed by FeMoco outside the protein and the results of earlier studies dealing with the dependence of the acetylene reduction rate on the thiophenol con centration [14] and with the stereospecificity of the reaction [15] demonstrate that the protonation of the acetylene molecule coordinated to the reduced cofac a p 1 K tor takes place in the [FeMoco-C 2 H 2 -proton donor ensemble] and the greater part of the ethylene results from intramolecular proton transfer from the pre pro tonated iron or sulfur atoms of the cofactor to the sub strate.…”

“…The totality of data for reactions involving FeMoco isolated from the protein suggests that the protonation of the acetylene molecule coordinated to the reduced cofactor occurs intramolecularly in the [FeMoco-C 2 H 2 -proton donor] complex. Earlier measurements of the acetylene reduction rate as a function of the thiophenol concentration [14] and an earlier study of the stereospecificity of the reaction [15] confirm that the greater part of ethylene results from intramolecular H transfer from protonated iron or sulfur atoms of the cofactor to the substrate.…”

“…The ammonia concentration was measured by the modified indophenol method [23]. For ammonia determination in the experiments involving labeled nitrogen 15 N 2 , 2.3 mL of the solution resulting from the nitrogen fixation reaction and 5 × 10 -5 mol of 15 NH 4 Cl were placed in one leg of a Rittenberg tube and 2 mL of a saturated sodium hypobromite solution was placed in the other one.…”

“…The integrity of the cluster framework after its isolation from the protein and after catalytic reactions involving FeMoco in nonprotein systems was esti mated as the ability of FeMoco to reproduce the enzy matic activity of the cofactor deficient MoFe protein of Klebsiella pneumoniae Kp5058. We demonstrated [12][13][14] that the iron-molybdenum cofactor is an active reduction catalyst for a variety of nitrogenase substrates in a dimethylformamide (DMF) medium containing a Zn or Eu amalgam as the reductant and thiophenol as the proton donor. To gain insight into the mechanism of the catalytic action of FeMoco in nonenzymatic systems, we carried out a detailed kinetic study of the FeMoco catalyzed reduction of nitrogenase substrates [11] and of the reaction of FeMoco with nitrogenase inhibitors.…”

Determination of ligand binding constants for the iron-molybdenum cofactor of nitrogenase: monomers, multimers, and cooperative behavior

“…Ever since the iron-molybdenum cofactor (FeMoco) of Azotobacter vinelandii and Klebsiella pneumoniae nitrogenase was isolated [1], interest in the chemistry [2,3,4,5,6,7,8,9,10,11,12,13,14,15,16], electronic structure [17,18,19,20,21,22,23,24,25], and rational synthesis [26,27,28,29,30,31,32,33,34] of this heterometal cluster has been intense. After publication of the solution to the crystal structure of the nitrogenase enzyme [35,36], this interest became structurally more explicit [13,37,38,39,40].…”