How cofactor-free oxygenases can overcome spin prohibition in substrates oxygenation by dioxygen

Abstract

Oxidases and oxygenases can activate the triplet ground state O2 molecule for the controlled chemical synthesis initiated by virtue of electron-transfer process which leads to dioxygen reduction. Typically they use organic cofactor or paramagnetic metal ion to initiate dioxygen activation and overcome spin prohibition for triplet O2 reactivity. A number of mono- and di-oxygenases are found recently which can operate even in the absence of any cofactor. Analysis of spin-orbit coupling in such enzymes helps to unravel some mechanistic puzzles and explains why aromatic substrate works instead cofactor. A general attribute of such enzymes, O2− radical, provides a good opportunity to induce internal magnetic perturbation and fulfill the spin flip as a common way to overcome spin prohibition for dioxygen activation. The driving force for spin flip – spin-orbit coupling inside superoxide ion – does not depend on the radical-pair partner; thus π-delocalized substrate can operate instead of flavin cofactor.