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PubMed2001

Industrial biocatalysis today and tomorrow.

The use of biocatalysis for industrial synthetic chemistry is on the verge of significant growth. Biocatalytic processes can now be carried out in organic solvents as well as aqueous environments, so that apolar organic compounds as well as water-soluble compounds can be modified selectively and efficiently with enzymes and biocatalytically active cells. As the use of biocatalysis for industrial chemical synthesis becomes easier, several chemical companies have begun to increase significantly the number and sophistication of the biocatalytic processes used in their synthesis operations.

Catalysis↗

PubMed1995

Extremozymes: expanding the limits of biocatalysis.

The study of enzymes isolated from organisms inhabiting unconventional ecosystems has led to the realization that biocatalysis need not be constrained to mild conditions and can be considered at pH's, temperatures, pressures, ionic and solvent environments long thought to be destructive to biomolecules. Parallel to this, it has been demonstrated that even conventional enzymes will catalyze reactions in solvents other than water. However, the intrinsic basis for biological function under extreme conditions is only starting to be addressed, as are associated applications. This was the focus of a recent NSF/NIST-sponsored workshop on extremozymes. Given the information acquired from the study of extremozymes, modification of enzymes to improve their ranges of stability and activity remains a possibility. Ultimately, by expanding the range of conditions suitable for enzyme function, new opportunities to use biocatalysis will be created.

Catalysis↗

PubMed2003

Dispelling the myths--biocatalysis in industrial synthesis.

Biocatalysis has emerged as an important tool in the industrial synthesis of bulk chemicals, pharmaceutical and agrochemical intermediates, active pharmaceuticals, and food ingredients. However, the number and diversity of the applications are modest, perhaps in part because of perceived or real limitations of biocatalysts, such as limited enzyme availability, substrate scope, and operational stability. Recent scientific breakthroughs in genomics, directed enzyme evolution, and the exploitation of biodiversity should help to overcome these limitations. As a result, we expect many new industrial applications of biocatalysis to be realized, from single-step enzymatic conversions to customized multistep microbial synthesis by means of metabolic pathway engineering.

Biotechnology↗

PubMed1994

Microbial biocatalysis in the generation of flavor and fragrance chemicals.

Microbial biocatalysis is used in the commercial production of many flavor and fragrance chemicals. Bulk flavoring chemicals such as citric acid, high fructose corn syrup, and glutamic acid are produced in millions of pounds annually using microbial processes. In the past few years, biocatalysis has also begun to play an increasingly important role in the production of many flavor and fragrance aroma chemicals. Microbial processes have traditionally played an integral role in the development of complex mixtures of flavor and aroma chemicals since the discovery of beer, wine, cheese, and soy sauce thousands of years ago. Today, contemporary microbiological techniques are being increasingly applied to enhance the efficiency of many microbial biocatalysts for the production of specific flavor and fragrance chemicals. However, to ensure commercial implementation of these new microbial processes, much more needs to be learned about the basic biochemistry and genetics of these novel biocatalysts.

Bacteria↗

PubMed1994

[Role of biocatalysis in the creation and improvement of production of beta-lactam antibiotics in Russia].

The paper presents the results of the studies carried out by the authors within 20 years on development of processes for production of beta-lactam antibiotics with using biocatalysis. The proposed general principles for the development of efficient biocatalytic technologies are discussed in regard to production of the key compounds and synthesis of beta-lactams. The paper includes 4 parts concerned with comparison of the biocatalytic and chemical processes for production of beta-lactam antibiotics, requirements to the quality of the biocatalysts used and criteria for estimation of the efficiency of the stage of the technological biocatalyst production. The criteria provided determination of the optimal biocatalyst for production of the key compounds in the synthesis of beta-lactams. A retrospective analysis of the biocatalytic processes for production of 6-amino-penicillanic acid is presented and the impact of the activity and the form of the biocatalyst on the process efficiency is substantiated. Various schemes of the enzymatic synthesis of beta-lactam antibiotics and the approaches to the improvement of the technological processes including those with the use of immobilized microbial cultures at the stage of the production of the initial biosynthetic antibiotics are described. The prospects for the improvement of the processes for production of drugs with the use of biocatalysis are indicated and the main trends of the research required for the large scale use of the immobilized enzymes, microbial cells, oligo-enzymatic and poly-enzymatic systems in transformation and synthesis of organic compounds are defined.

Anti-Bacterial Agents↗

PubMed2001

Predicting when precipitation-driven synthesis is feasible: application to biocatalysis.

Precipitation-driven synthesis offers the possibility of obtaining high reaction yields using very low volume reactors and is finding increasing applications in biocatalysis. Here, a model that allows straightforward prediction of when such a precipitation-driven reaction will be thermodynamically feasible is presented. This requires comparison of the equilibrium constant, Keq, with the saturated mass action ratio, Zsat, defined as the ratio of product solubilities to reactant solubilities. A hypothetical thermodynamic cycle that can be used to accurately predict Zsat, in water is described. The cycle involves three main processes: fusion of a solid to a supercooled liquid, ideal mixing of the liquid with octanol, and partitioning from octanol to water. To obtain the saturated mass action ratio using this cycle, only the melting points of the reactants and products, and in certain cases the pKa of ionisable groups, are required as input parameters. The model was tested on a range of enzyme-catalysed peptide syntheses from the literature and found to predict accurately when precipitation-driven reaction was possible. The methodology employed is quite general and the model is therefore expected to be applicable to a wide range of other (bio)-catalysed reactions.

Amides↗

PubMed2002

Bis(mu-oxo)dimetal "diamond" cores in copper and iron complexes relevant to biocatalysis.

Although quite a familiar feature in high-valent manganese chemistry, the M(2)(mu-O)(2) diamond core motif has only recently been found in synthetic complexes for M=Cu or Fe. Structural and spectroscopic characterization of these more reactive Cu(2)(mu-O)(2) and Fe(2)(mu-O)(2) compounds has been possible through use of appropriately designed supporting ligands, low-temperature handling methods, and techniques such as electrospray ionization mass spectrometry and X-ray crystallography with area detector instrumentation for rapid data collection. Despite differences in electronic structures that have been revealed through experimental and theoretical studies, Cu(2)(mu-O)(2) and Fe(2)(mu-O)(2) cores exhibit analogously covalent metal-oxo bonding, remarkably congruent Raman and extended X-ray absorption fine structure (EXAFS) signatures, and similar tendencies to abstract hydrogen atoms from substrates. Core isomerization is another common reaction attribute, although different pathways are traversed; for Fe, bridge-to-terminal oxo migration has been discovered, while for Cu, reversible formation of an O-O bond to yield a peroxo isomer has been identified. Our understanding of biocatalysis has been enhanced significantly through the isolation and comprehensive characterization of the Cu(2)(mu-O)(2) and Fe(2)(mu-O)(2) complexes. In particular, it has led to the development of new mechanistic notions about how non-heme multimetal enzymes, such as methane monooxygenases, fatty acid desaturase, and tyrosinase, may function in the activation of dioxygen to catalyze a diverse array of organic transformations.

Catalysis↗

PubMed2000

Biocatalysis for pharmaceuticals--status and prospects for a key technology.

In reviewing how biocatalysis can be applied to improve chiral synthesis for pharmaceuticals it becomes clear that there will be many opportunities using a simple enzyme system but that many of the more useful applications will require the whole cell because of the requirement for cofactors. An assessment is made of the opportunities to apply metabolic engineering to construct de novo metabolic pathways for the biosynthesis of useful advanced intermediates and a conceptual example is provided for the biosynthesis of cis-aminoindanol. We predict that in the future novel pathways will be assembled for a one-step biosynthesis of many semisynthetic natural products.

Animals↗

PubMed1993

Whole cell biocatalysis in nonconventional media.

In this paper biocatalytic reactions carried out by whole cells in nonconventional media are reviewed. Similar relationships are observed between solvent hydrophobicity and catalytic activity in reactions carried out by isolated enzymes and whole cells. In addition to the effect of organic solvent on biocatalyst stability, microbial cells are susceptible to damaging effects caused by the organic phase. In general, more hydrophobic solvents manifest lower toxicity towards the cells. Whole cell biocatalysts require more water than isolated enzymes and two-phase systems have been most widely used to study whole cell biocatalysis. Immobilization makes cell biocatalysts more resistant to organic solvents and helps achieve homogeneous biocatalyst dispersion. Cell entrapment methods have been widely used with organic solvent systems and mixtures of natural and/or synthetic polymers allow adjustment of the hydrophobicity-hydrophilicity balance of the support matrix. Some examples of stereoselective catalysis using microbial cells in organic solvent media are presented.

Bacteria↗

PubMed2004

Directed evolution of enzymes for biocatalysis and the life sciences.

Engineering the specificity and properties of enzymes and proteins within rapid time frames has become feasible with the advent of directed evolution. In the absence of detailed structural and mechanistic information, new functions can be engineered by introducing and recombining mutations, followed by subsequent testing of each variant for the desired new function. A range of methods are available for mutagenesis, and these can be used to introduce mutations at single sites, targeted regions within a gene or randomly throughout the entire gene. In addition, a number of different methods are available to allow recombination of point mutations or blocks of sequence space with little or no homology. Currently, enzyme engineers are still learning which combinations of selection methods and techniques for mutagenesis and DNA recombination are most efficient. Moreover, deciding where to introduce mutations or where to allow recombination is actively being investigated by combining experimental and computational methods. These techniques are already being successfully used for the creation of novel proteins for biocatalysis and the life sciences.

Catalysis↗

PubMed2003

Regeneration of cofactors for use in biocatalysis.

Cofactor-dependent enzymes catalyze many synthetically useful reactions. The high cost of cofactors, however, necessitates in situ cofactor regeneration for preparative applications. After two decades of research, several cofactors can now be effectively regenerated using enzyme or whole-cell based methods. Significant advances have been made in this area in the past three years and include the development of novel or improved methods for regenerating ATP, sugar nucleotides and 3-phosphoadenosine-5'-phosphosulphate. These approaches have found novel applications in biocatalysis.

Adenosine Triphosphate↗

PubMed2005

Biocatalysis in semi-aqueous and nearly anhydrous conditions.

In the past few years there have been prolific advances in activating enzymes for nonaqueous biocatalysis. Molecular dynamics simulations complement recent experimental results and offer new insights into the deleterious effects of organic solvents, such as water stripping and active-site penetration. Methods for activating enzymes in semi-aqueous or nonaqueous media include protein engineering, chemical modification, and co-lyophilization with non-buffer salts. Enzyme immobilization on novel polymeric supports and the use of zeolite molecular sieves can also increase solvent tolerance, enhance activity, and improve enantioselectivity. The recent implementation of enzymes in ionic liquids has also led to better long-term stability relative to traditional organic solvents and the simultaneous solubilization of enzymes, cofactors and substrates.

Catalysis↗

PubMed2005

Biodiesel production from triolein and short chain alcohols through biocatalysis.

Oleic acid alkyl esters (biodiesel) were synthesised by biocatalysis in solvent-free conditions. Different commercial immobilised lipases, namely Candida antarctica B, Rizhomucor miehei, and Pseudomonas cepacia, were tested towards the reaction between triolein and butanol to produce butyl oleate. Pseudomonas cepacia lipase resulted to be the most active enzyme reaching 100% of conversion after 6h. Different operative conditions such as reaction temperature, water activity, and reagent stoichiometric ratio were investigated and optimised. These conditions were then used to investigate the effect of linear and branched short chain alcohols. Methanol and 2-butanol were the worst alcohols: the former, probably, due to its low miscibility with the oil and the latter because secondary alcohols usually are less reactive than primary alcohols. Conversely, linear and branched primary alcohols with short alkyl chains (C(2)--C(4)) showed high reaction rate and conversion. A mixture of linear and branched short chain alcohols that mimics the residual of ethanol distillation (fusel oil) was successfully used for oleic acid ester synthesis. These compounds are important in biodiesel mixtures since they improve low temperature properties.

Alcohols↗

PubMed2006

Water immiscible ionic liquids as solvents for whole cell biocatalysis.

Whole cell biocatalysis can effectively be used for the production of enantiomerically pure compounds, but efficiency is often low. Toxicity and poor solubility of substrates and products are the main obstacles. In this study, water immiscible ionic liquids are shown to have no damaging effects on the cell membranes of Escherichia coli and Saccharomyces cerevisiae. Thus, they can be used as biocompatible solvents for microbial biotransformations exemplified by an increase in yield of chiral alcohol synthesis. As key point to the success of these processes, the distribution ratio of the reactants between the ionic liquid and the aqueous phase was identified. The use of ionic liquids as substrate reservoir and in situ extracting agent for the asymmetric reduction of various ketones resulted in an increase of chemical yield from <50% to 80-90% in simple batch processes. (R)-1-(4-chlorophenyl)ethanol was produced at a higher initial reaction rate in the biphasic system (>50 microM s(-1) L(-1)) compared to the aqueous system. This result demonstrates that good mass transfer rates can be obtained despite the relatively high viscosity of ionic liquids.

Biocompatible Materials↗

PubMed2006

Computational methods to rationalize experimental strategies in biocatalysis.

Computational methods are more and more widely applied in biocatalysis to gain rational guidelines, to orient experimental planning and, ultimately, to avoid expensive and time-consuming experiments. In this respect, molecular modelling, multivariate statistical analysis and chemometrics in general are useful computational tools, although they follow completely different investigative approaches.

Biotechnology↗

PubMed1999

Programming of enzyme specificity by substrate mimetics: investigations on the Glu-specific V8 protease reveals a novel general principle of biocatalysis.

In this paper the universal validity of the substrate mimetic concept in enzymatic C-N ligations was expanded to anionic leaving groups based on the specificity determinants of Glu-specific endopeptidase from Staphylococcus aureus (V8 protease). In an empirical way a specific mimetic moiety was designed from simple structure-function relationship studies. The general function of the newly developed substrate mimetics to serve as an artificial recognition site for V8 protease have been examined by hydrolysis kinetic studies. Enzymatic peptide syntheses qualify the strategy of substrate mimetics as a powerful concept for programming the enzyme specificity in the direction of a more universal application of enzymes in the general area of biocatalysis.

Acylation↗

PubMed2003

Biocatalysis in ionic liquids - advantages beyond green technology.

In recent years researchers have started to explore a particular class of organic solvents called room temperature ionic liquids - or simply ionic liquids - to identify their unique advantages for biocatalysis. Because they lack vapour pressure, ionic liquids hold potential as green solvents. Furthermore, unlike organic solvents of comparable polarity, they often do not inactivate enzymes, which simplifies reactions involving polar substrates such as sugars. Biocatalytic reactions in ionic liquids have also shown higher selectivity, faster rates and greater enzyme stability; however, these solvents present other challenges, among them difficulties in purifying ionic liquids and controlling water activity and pH, higher viscosity and problems with product isolation.

Catalysis↗

PubMed1999

Dehalogenases applied to industrial-scale biocatalysis.

In the recent past, the development of dehalogenating enzymes for industrial biocatalysis has been limited, but significant advances have been made. Three classes of enzymes have received attention and development: halalkanoic acid dehalogenases (EC 3.8.1.2), hydrogen-halide lyases (EC 4.5.1), and haloalkane dehalogenases (EC 3.8.1). Applications range from the manufacture of chiral intermediates, to recycling of chlorinated byproducts from chemical manufacturing, and selective treatment of process waste streams.

Biodegradation, Environmental↗