Quantitative structure activity relationships for the electron transfer reactions of Anabaena PCC7119 ferredoxin-NADP(+) oxidoreductase with nitrobenzene and nitrobenzimidazolone derivatives: mechanistic implications

The steady state single electron reduction of polynitroaromatics by ferredo xin-NADP(+) oxidoreductase (EC 1.18.1.2) from cyanobacterium,Anabaena PCC 7 119 has been studied and quantitative structure activity relationships are described. The solubility of the polynitroaromatics as well as their reacti vity towards ferredoxin-NADP(+) oxidoreductase are markedly higher than tho se for previously studied mononitroaromatics and this enabled the independe nt measurement of the kinetic parameters-k(cat) and K-m. Interestingly, the natural logarithm of the bimolecular rate constant, k(cat)/K-m, and also t he natural logarithm of k(cat) correlate with the calculated energy of the lowest unoccupied molecular orbital of the polynitroaromatic substrates, Th e minimal kinetic model in line with these quantitative structure activity relationships is a ping-pong mechanism which includes substrate binding equ ilibria in the second half reaction, (C) 1999 Federation of European Bioche mical Societies.