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 ferredoxin-NADP(+) oxidoreductase (EC 1.18.1.2) from cyanobacterium,Anabaena PCC 7119 has been studied and quantitative structure activity relationships are described. The solubility of the polynitroaromatics as well as their reactivity towards ferredoxin-NADP(+) oxidoreductase are markedly higher than those for previously studied mononitroaromatics and this enabled the independent 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 the natural logarithm of k(cat) correlate with the calculated energy of the lowest unoccupied molecular orbital of the polynitroaromatic substrates, The minimal kinetic model in line with these quantitative structure activity relationships is a ping-pong mechanism which includes substrate binding equilibria in the second half reaction, (C) 1999 Federation of European Biochemical Societies.