Biochemical transformations medium

Photoswitchable enzymes could have an important role in controlling biochemical transformations in bioreactors. Various biotechnological processes generate an inhibitor, or alter the environmental conditions (pH, for example) of the reaction medium. Photochemical activation of enzymes that adjust environmental conditions or deplete the inhibitor to a low concentration may maintain the bioreactor at optimal performance. More specifically, integration of the photoswitchable biocataly-tic matrix with a sensory electrode might yield a feedback mechanism in which the sensor element triggers the light-induced activation/deactivation of the photosensitive biocatalyst. 

Both methods, however, have disadvantages. Biochemical transformations can have limited application, and there is always the problem of finding the proper bacteria, animal preparation, or enzyme and culture medium to effect a new synthesis. In addition, product isolation—such as in the production of an optically active < -deuteroalcohol, where a small amount of product must be isolated from a large quantity of spent fermentation liquor—can present formidable separation problems. Product isolation from enzyme systems, especially immobilized enzymes, could be much simpler, however. 

More specifically, in the 1950s, McLaren reported the pioneering discovery that the fermentation yield of vitamin B2 in cultures of Eremothecium ashhyii (then in the range of milligram per liter) could be increased by the addition of naturally occurring purines such as adenine to the culture medium." A flurry of papers subsequently demonstrated that the atoms of the purine ring system, with the exception of C-8, could actually become part of the vitamin by biochemical transformation. 

The rates of the biochemical transformations that take place in a bioreactor are proportional to the quantity of biomass present. If we presume that species S is the substrate whose concentration in the growth medium limits the extent of reaction, the rate of consumption of this species per unit quantity of biomass can usually be expressed as... 

The results obtained in Illustration 13.1 indicate that for the biochemical reaction of interest the biomass specific growth rate is essentially constant. This fact, in turn, implies that the parameter Kg in the Monod equation is sufficiently small that it can neglected over the large majority of the time that the biochemical transformation is taking place. Under these circumstances a mass balance for the microorganism leads to the following developments for circumstances when the volume of the growth medium remains constant ... 

Aromatic and heteroaromatic nitriles were selectively transformed into the corresponding amides by a Rhodococcus rhodochrous strain [663] the products accumulated in the culture medium in significant amounts (Scheme 2.103). In contrast to the hydrolysis performed by chemical means, the biochemical transformations were highly selective and occurred without the formation of the corresponding carboxylic acids. 

Another relatively simple system for the epoxidation of tri- and c/r-disubstituted olefins is formamide-hydrogen peroxide in an aqueous medium. This reagent has the advantage of being pH-independent, which makes it attractive for biochemically mediated transformations. No reaction was observed in the case of /ran.v-disubstituted and terminal olefins. With bifunctional alkenes, the more reactive double bond is selectively epoxidized [95TL4015]. 

A relatively simple case is when one well-known compound is determined in a given product. Examples are determination of an antioxidant, vitamin, or colorant in a food product or of a plant protection compound in a specified agricultural object. The situation becomes complicated when there is the probability of chemical transformation of the analyte in the sample, as happens frequently during determination of a drug, toxin, or narcotic in urine, blood, or other biological object. In such cases, it is necessary to take into account probable biochemical processes occurring in a given medium, with formation of initially unsuspected metabolites with a priori unknown composition. 

Many tumor viruses have a particularly valuable property. They elicit cancerous changes in cells in an artificial culture medium. This transformation makes it possible to examine thoroughly interactions under controlled conditions, avoiding difficulties associated with experiments on animals, though some viruses are powerful oncogenic agents in animals and do not transform culture cells. The process of transformation includes important morphologic and biochemical... 

The application of hairy root culture technology is valuable for the production of compounds that are synthesized in roots, including the tropane alkaloids [4]. These cultures are characterized by its genetic and biochemical stability, rapid growth in hormone-free medium as well as the possibility of genetic manipulation [57]. It is generally believe that the secondary metabolites produced by hairy root cultures are the same as those synthesized by non-transformed roots and are produced with the same or even higher yields [6]. 

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