Molybdenum-Containing Enzymes and Their Applications (pp. 117-146)
Authors: (F. Özde Ütkür, Bruno Bühler, Laboratory of Chemical Biotechnology, Department of Biochemical and Chemical Engineering, TU Dortmund University, Dortmund, Germany)
Abstract: In nature, molybdenum (Mo) is an essential trace metal for most biological systems ranging from prokaryotes to green plants and animals. Once Mo enters the cells in the bioavailable form as molybdate (MoO4-2), it is subsequently incorporated into a metal cofactor, which makes it biologically active. In this active form, Mo plays a key role as an electron carrier in enzymes involved in carbon, sulphur, and nitrogen metabolism. Among the wealth of biological redox reactions catalyzed by oxidoreductases, Mo-containing enzymes are especially versatile in the catalysis of oxygen transfer from or to a substrate.
In the former case, this includes nitrate and DMSO reductases involved in respiratory processes, which catalyze oxygen abstraction in the form of water. In the latter case, water serves as oxygen donor for the oxidation of a variety of substrates including sulfite, aldehydes, and aromatic (hetero)cycles. Up to date, studies on Mo-enzymes focused more on structural, spectroscopic, and functional aspects. After giving an overview on biological functions and molecular mechanisms, this chapter will focus on the industrial and technical application potential of Mo-containing enzymes. Here, hydroxylation reactions are of special interest, because water constitutes a very cheap and mild oxygen donor in contrast to peroxides (peroxidases, chemical methods) or molecular oxygen (oxygenases) which give rise to reactive oxygen species, destabilizing the catalyst and/or leading to side reactions. Present applications and reactions with high application potential are discussed.
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