Biocatalyst productivity

Typically, a biocatalytic process for oil refining involves several stages beginning with biocatalyst production. This involves growth of the microorganism via fermentation... 

For R. erythropolis KA2-5-1, DBT and 2-aminoethanesulfonicacid were compared as the sole sulfur source for growth with ethanol as carbon source. The 2-aminoethanesulfonicacid was found to be a better sulfur source (for growth) than DBT [189], A summary of the various studies investigating biocatalyst production are given in Table 10. It is clear that a balance between the growth rate and the sulfur utilization rate is necessary to obtain an optimum biocatalyst. Preventing accumulation of sulfate is the key to optimum activity of the final biocatalyst preparation. Thus, a... 

In addition to desulfurization activity, several other parameters are important in selecting the right biocatalyst for a commercial BDS application. These include solvent tolerance, substrate specificity, complete conversion to a desulfurized product (as opposed to initial consumption/removal of a sulfur substrate), catalyst stability, biosurfactant production, cell growth rate (for biocatalyst production), impact of final desulfurized oil product on separation, biocatalyst separation from oil phase (for recycle), and finally, ability to regenerate the biocatalyst. Very few studies have addressed these issues and their impact on a process in detail [155,160], even though these seem to be very important from a commercialization point of view. While parameters such as activity in solvent or oil phase and substrate specificity have been studied for biocatalysts, these have not been used as screening criteria for identifying better biocatalysts. 

Biocatalysts Ltd. is an independent company that since 1980 has been devoted to the manufacture and sales enzymes. Since it is not part of a larger chemical, food ingredients or pharmaceutical company, instead of producing large volumes of commodity enzymes, it produces enzymes tailored to customer needs. Their services include working together with customers to industrialize their processes or to produce specific required enzymes. Usually, these customer sectors do not require single enzyme entities, but enzyme complexes where the ratios of each of the components are crucial to the efficacy of the whole enzyme-biocatalyst product and to the customer s process. Fermentation requirements for the manufacture of enzyme products are sub-contracted out. 

Conversions of primary feedstocks by fermentations (such as glucose to ethanol) are not included in this book. However, fermentations are usually required to produce the enzymes or cells in the first place, and therefore chapter 5 includes a review of this type of fermentation. Chapter 5 also covers the other aspects of biocatalyst production, except immobilization and protein and genetic engineering, which are treated in chapter 6 and 7, respectively. 

In the preceding section, we analyzed an immobilized enzyme process and calculated some important parameters such as productivity. In this section, we investigate another process configuration for retaining biocatalysts, the membrane reactor. The advantages and disadvantages of immobilization and membrane retention have already been discussed in Chapter 5. As in the case of immobilization, retention of catalyst by a membrane vastly improves biocatalyst productivity, a feature important on a processing scale but usually not on a laboratory scale. 

Several biocatalytic processes for the production of (5)-(+)-naproxen (5) have also been developed (see Chapter 19). Direct isomerization of racemic naproxen (4) by a microorganism catalyst, Exophialia wilhansil, was reported to give the (S)-isomer 5 (92%, 100% ee) (Scheme 6.5).2X A 1-step synthesis of (5)-(+)-naproxen (5) by microbial oxidation of 6-methoxy-2-isopropylnaphthalene (12) was developed by IBIS (Scheme 6.6).29 In both cases, typical bioprocess-related issues such as productivity, product isolation, and biocatalyst production have apparently prevented them from rapid commercialization. 

Hydrolases were in the first catalogue after the company was founded in 1950 but, not surprisingly, the chiral molecules originated mainly from the chiral pool. The first biocatalytic reactions were developed with kidney acylases and later with esterases and lipases, in the beginning mainly animal-derived biocatalysts [10], The set-up of in-house biocatalyst production from microbial and plant sources as well as the construction of a new biotechnology laboratory with ten fermenters of up to 300 L total volume, allow the development and production of improved biocatalysts and for them to be applied in the asymmetric synthesis of laboratory chemicals. There are today more than 100 biocatalytic processes in routine production and a project management team is handling custom biotransformations. 

Consider the following Uni Uni biocatalysis kinetic scheme that involves two biocatalyst-substrate species intermediates that are generated prior to product formation and release (Scheme 8.15). Most of the steps involve the inter-conversions of biocatalyst-substrate or biocatalyst-product species and hence microscopic inter-conversion rates will depend only upon single-species concentrations. In other words, these inter-conversions must obey first order kinetics. Similarly, if S and E are combined under conditions where [S] [E], such that [S] is effectively unchanged during reaction, then the microscopic inter-conversion rate from E to ES will once again depend effectively only upon [E] such that this inter-conversion obeys pseudo-first-order kinetics. Accordingly, every step/inter-conversion shown in the biocatalysis reaction scheme above obeys and could be analysed by appropriate variations of Equation (8.80). 

Novella IS, Fargues C, GreviUot G (1994) Improvement of extraction of penicillin acylase by a combined use of chemical methods. Biotechnol Bioeng 44 379-382 Ospina S, Lopez-Mungufa A, GonztQez R et al. (1992) Characterization and use of a penicillin acylase biocatalyst. J. Chem Technol Biotechnol 53 205-214 Ospina SS, Merino E, Ramirez OT et til. (1995) Recombinant whole cell penicillin acylase biocatalyst production, characterization and use in the synthesis and hydrolysis of antibiotics. Biotechnol Lett 17 615-620... 

Another advantage of extremely thermophilic enzymes is that when they are produced recombinantly in mesophilic hosts, heat treatment serves as an efficient method to purify the target enzyme from the host s proteins, which readily denature at higher temperatures (21). This strategy can be used to great advantage for biocatalyst production. 

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