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Category: Applied and Industrial Microbiology; Environmental Microbiology
Diversity, Function, and Biocatalytic Applications of Alkane Oxygenases, Page 1 of 2
< Previous page | Next page > /docserver/preview/fulltext/10.1128/9781555817589/9781555813277_Chap13-1.gif /docserver/preview/fulltext/10.1128/9781555817589/9781555813277_Chap13-2.gifAbstract:
This chapter focuses on the aerobic degradation of hydrocarbons, with an emphasis on alkanes, and the applications of enzymes involved in these processes for biocatalysis. Yeasts and fungi are often mentioned as alkane degraders, for example in connection with the production of single-cell proteins or organic acids and amino acids from hydrocarbons. Soluble and particulate mono-oxygenases are known to oxidize the same compounds, and some of the gene diversity detected with primers that amplify membrane-bound methane mono-oxygenase (pMMO) and soluble MMO (sMMO) genes may well be due to short-chain alkane-degrading bacteria instead of methanotrophs. The application of oxygenases in biocatalytic processes is more complicated than that of enzymes such as hydrolases, because of cofactor and oxygen requirements, the sensitive nature of many oxygenases, the toxicity of substrates and products to the biocatalyst, and the uptake of the lipophilic substrates. The best strain in this study was a hexane-degrading Sphingomonas sp. strain HXN-200, isolated from a trickling-bed bioreactor. The oxygenases that are required for the initial activation of alkanes belong to several different enzyme classes, some of which act on medium- and long-chain alkanes, while others oxidize only short-chain alkanes. Studies of alkane hydroxylase (AH) gene diversity, coupled with information on substrate range, induction, enzyme kinetics, and host properties, should help in understanding and optimizing the biodegradative activity of indigenous hydrocarbon-degrading strains, benefit biocatalytic applications, and promote fundamental research on the activation of oxygen by enzymes and biomimetic catalysts.
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Pathways for the degradation of alkanes by terminal, subterminal, and biterminal oxidation. Terminal oxidation leads to the formation of fatty acids, which enter the β-oxidation pathway. Alternatively, ω-hydroxylation by a fatty acid mono-oxygenase or AH may take place, leading to dicarboxylic acids. Subterminal oxidation gives rise to secondary alcohols, which are oxidized to a ketone. A Baeyer-Villiger mono-oxygenase converts the ketone to an ester, which is subsequently cleaved by an esterase. (Reprinted from Oil and Gas Science and Technology [ van Beilen et al, 2003b ] with permission of the publisher.)
Pathways for the degradation of alkanes by terminal, subterminal, and biterminal oxidation. Terminal oxidation leads to the formation of fatty acids, which enter the β-oxidation pathway. Alternatively, ω-hydroxylation by a fatty acid mono-oxygenase or AH may take place, leading to dicarboxylic acids. Subterminal oxidation gives rise to secondary alcohols, which are oxidized to a ketone. A Baeyer-Villiger mono-oxygenase converts the ketone to an ester, which is subsequently cleaved by an esterase. (Reprinted from Oil and Gas Science and Technology [ van Beilen et al, 2003b ] with permission of the publisher.)
Oxidation reactions catalyzed by AHs. See the text for details and references.
Oxidation reactions catalyzed by AHs. See the text for details and references.
Genera containing isolates that aerobically degrade aliphatic hydrocarbons a
Genera containing isolates that aerobically degrade aliphatic hydrocarbons a
Enzyme classes shown to be involved in the oxidation of alkanes a
Enzyme classes shown to be involved in the oxidation of alkanes a