Biocatalysis is the use of enzymes as catalysts. Unfortunately, the word “biocatalysis” often seems to invoke the thought that the principles of chemistry and thermodynamics are somehow different because a biological entity is being used. Enzymes are simply catalysts that are high molecular weight polyamides that do not usually contain a precious metal atom. The use of an enzyme (rather than a precious metal) to catalyze a reaction does not change the principles of chemistry, physics, biology, or thermodynamics. Enzymes lower the energy of activation of the desired reaction so that it proceeds faster than it would otherwise – exactly the same as any other catalyst, organic or inorganic. And like any other catalyst, an enzyme has a turnover number, a lifetime, a range of operating conditions and sensitivities, inhibitors, association constants of substrates and dissociation constants of products, specific catalytic activity, and other kinetic parameters, cost restrictions, immobilization, and other process and engineering requirements that would apply to any other catalyst. But the range of all these characteristics gives biocatalysis the flexibility to address processes that may not be amenable to non-biological catalysis.
Part of the problem with the perception of biocatalysis is that it is an extraordinarily interdisciplinary field and includes a number of concepts and topics. The most obvious discipline of the field is (or should be!) chemistry, i.e. the requirements of the reaction that one desires to catalyze, and the chemical and physical characteristics of the starting material and product. Of such characteristics, stereochemistry and functional group selectivity are generally considered the most important, and it is with respect to these properties that enzymes enjoy significant performance advantages over other catalysts. For example, an enzyme is available which can insert an oxygen atom into the inactivated carbon-hydrogen bond of a methylene group, selectively creating secondary alcohol, while not catalyzing any reaction of the ketones, alcohols, and olefins present in the same molecule. Further, this reaction proceeds with completely selective stereochemistry, inserting the oxygen atom into only one of the two carbon-hydrogen bonds on the methylene group.
Equally important, biocatalysis also includes the disciplines of molecular/synthetic biology and the methods available for manipulation of the catalyst, microbiology, and the requirements for the production of the catalyst, including the biology of the organism to be used, the fermentation process, and protein purification methods, and biochemistry in general, including the knowledge of the common, and uncommon, reactions that enzymes are known to catalyze in living systems, and where one might reasonably look to find a desired catalytic activity for a new reaction.
The process engineering aspects of the field are also of considerable breadth. Biocatalysis may be performed by single, isolated enzymes, and this can be done in either aqueous or non-aqueous media. Combinations of enzymes that catalyze a number of sequential reactions are known, and indeed, entire pathways may be assembled for transforming a starting material into the desired product. Biocatalysis can be achieved using whole cells that are either actively growing in a fermentation vessel to which both nutrients and the substrate are fed, or by cells held in a resting state by nutrient restriction in a variety of physical containment configurations.
The combination of disciplines comprising the field of bio-catalysis is extremely powerful but requires an interdisciplinary perspective to be fully exploited. The best renewable energy and biochemical consulting firms will have qualified bio-catalysis expertise, especially if they provide bio litigation support.
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