Autor: T. A. Bazhenova, G. N. Petrova, S. A. Mironova, M. A. Bazhenova
Rok vydání: 2002
Předmět:
Zdroj: Kinetics and Catalysis. 43:199-209
ISSN: 0023-1584
DOI: 10.1023/a:1015316427248
Popis: The inhibiting effects of CO and N2 on the ability of the nitrogenase iron–molybdenum cofactor (FeMoco) to catalyze acetylene reduction outside the protein were studied to obtain data on the mechanism of substrate reduction at the active center of the enzyme nitrogenase. It was found that CO and N2 reacted with FeMoco that was separated from the enzyme and reduced by zinc amalgam (E = –0.84 V with reference to a normal hydrogen electrode (NHE)) (I) or europium amalgam (E = –1.4 V with reference to NHE) (II). In system I, CO reversibly inhibited the reaction of acetylene reduction to ethylene with Ki = 0.05 atm CO. In system II, CO inhibited the formation of the two products of C2H2 reduction in different manners: the mixed-type or competitive inhibition of ethylene formation with Ki = 0.003 atm CO and the incomplete competitive inhibition of ethane formation with Ki = 0.006 atm CO. The fraction of C2H6 in the reaction products was higher than 50% at a CO pressure of 0.05 atm because of the stronger inhibiting effect of CO on the formation of C2H4. A change in the product specificity of acetylene-reduction centers under exposure to CO was explained by some stabilization of the intermediate complex [FeMoco · C2H2] upon the simultaneous coordination of CO to the catalytic cluster. Because of this, the fraction of the many-electron reduction product (ethane) increased. The experimental results suggest that several active sites in the FeMoco cluster reduced outside the protein can be simultaneously occupied by substrates and (or) inhibitors. The inhibition of both ethane and ethylene formation by molecular nitrogen in system II is competitive with Ki = 0.5 atm N2 for either product. That is, N2 and C2H2 as ligands compete for the same coordination site in the reduced FeMoco cluster. The inhibiting effects of CO and N2 on the catalytic behaviors of FeMoco outside the protein and as an enzyme constituent were compared.
Databáze: OpenAIRE
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