Applied Microbiology and Biotechnology

, Volume 60, Issue 3, pp 243–257

Oxygenases without requirement for cofactors or metal ions

  •  S. Fetzner

DOI: 10.1007/s00253-002-1123-4

Cite this article as:
Fetzner, S. Appl Microbiol Biotechnol (2002) 60: 243. doi:10.1007/s00253-002-1123-4


Mono- and dioxygenases usually depend on a transition metal or an organic cofactor to activate dioxygen, or their organic substrate, or both. This review points out that there are at least two separate families of oxygenases without any apparent requirement for cofactors or metal ions: the quinone-forming monooxygenases which are important 'tailoring enzymes' in the biosynthesis of several types of aromatic polyketide antibiotics, and the bacterial dioxygenases involved in the degradation of distinct quinoline derivatives, catalyzing the 2,4-dioxygenolytic cleavage of 3-hydroxy-4-quinolones with concomitant release of carbon monoxide. The quinone-forming monooxygenases might be useful for the modification of polyketide structures, either by using them as biocatalysts, or by employing combinatorial biosynthesis approaches. Cofactor-less oxygenases present the mechanistically intriguing problem of how dioxygen is activated for catalysis. However, the reactions catalyzed by these enzymes are poorly understood in mechanistic terms. Formation of a protein radical and a substrate-derived radical, or direct electron transfer from a deprotonated substrate to molecular oxygen to form a caged radical pair may be discussed as hypothetical mechanisms. The latter reaction route is expected for substrates that can easily donate an electron to dioxygen, and requires the ability of the enzyme to stabilize anionic intermediates. Histidine residues found to be catalytically relevant in both types of cofactor-less oxygenases might be involved in substrate deprotonation and/or electrostatic stabilization.

Copyright information

© Springer-Verlag 2002

Authors and Affiliations

  •  S. Fetzner
    • 1
  1. 1.AG Mikrobiologie, ICBM, Carl von Ossietzky Universität Oldenburg, Postfach 2503, 26111 Oldenburg, Germany