Biocatalysis . Biological systems for the production of chemicals *
نویسنده
چکیده
Biocatalysis harnesses the catalytic potential of enzymes to produce building blocks and end-products for the pharmaceutical and chemical industry. Located at the interface between fermentation processes and petrol-based chemistry, biotransformation processes broaden the toolbox for bioconversion of organic compounds to functionalized products. BIOCATALYSIS AND BIOTRANSFORMATION CONNECT PETROL-BASED CHEMICALS AND RENEWABLE CARBON SOURCES Improvement of synthetic routes according to the guidelines of green chemistry requires increased reaction specificities, reduction of solvent use and emissions, and the use of renewable resources. At first glance, these measures primarily aim at protection of the environment. However, green chemistry also makes economical sense, due to considerable savings on wastewater treatment, energy use, and organic carbon resources. The latter aspects bear directly on the problems associated with our decreasing fossil organic carbon stocks. A recently published analysis of the life-time of the organic carbon feed stocks indicates that the maximal production rates of crude oil will be reached in the next 10 to 20 years [1]. Alternative stocks such as Canada’s oil tars might be available by then [2], but an increase of the oil price in the next few decades is to be anticipated. Alternative energy sources and new sources for building blocks for chemical synthesis have to be developed. At this point it should be emphasized that a significant share of today’s oil production is needed for synthetic chemistry. The EU uses 57 MMT (approx. 8% of the total consumption of the EU) as organic carbon feedstock [3]. A key technology to facilitate and smooth the necessary transition is the use of renewable resources for the production of chemicals using biocatalytic processes. These processes can be subdivided into biotransformation reactions in which a reaction precursor, renewable or petrol-based, is converted to the desired product, and fermentations that use the carbon source for de novo product synthesis, usually from a renewable carbon source (Fig. 1). Fermentation processes are commonly used for transformation of renewable carbon to typical “biological” compounds such as alcohols, ketones, vitamins, antibiotics, or amino acids, which are metabolites or dead-end products in the production organism. As a matter of fact, the range of fermentation products is much broader than commonly realized. Compounds usually perceived as non-natural such as, for example, indigo, catechol, hexanoic acid, or poly-(b)-hydroxyalkanoates can be produced from renewable carbon as well. However, the biochemical and genetic engineering that is required for the development of mature processes from early observations on the lab-scale is demanding. Therefore, the total number of compounds that are produced by fermentation today is still relatively limited. Biocatalytic processes employ a different strategy. Precursor molecules are fed to the biocatalyst, which transforms them to the desired compound by a limited number of functionalizing steps (usually one). Carbon and energy required for production of the biocatalyst commonly come from a different, easily metabolizable carbon source such as a sugar. Here, the range of products is not limited by the metabolism of the biocatalyst: non-natural (xenobiotic) precursor molecules can be efficiently trans-
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