Enzymes in biotransformation

In this section, the advantages of the use of whole cells over the use of isolated enzymes in biotransformation processes are presented. 

The application of isolated enzymes in biotransformations is often superior to the use of cell-systems, since the various enzymes existing in living cells may result in the formation of by-products and thus cause side-reactions of the substrates and impair the yield of the desired products. 

DE1G Crout, S Davies, RJ Eleath, CO Miles, DR Rathbone, BEP Swoboda. Application of hydrolytic and decarboxylating enzymes in biotransformations. Biocatalysis 9 1-30, 1994. 

Figure 2.16 (a) Keyelementsin bioprocessing (b) frequency of use of enzymes in biotransformations. Source adapted from Faber [145],... 

Pure enzymes are usually very expensive and are thus mostly sold by the unit, while crude preparations are often shipped in kg amounts. Since the techniques for protein purification through His- or Strep-tagging are becoming easier and more economic, the use of (partially) purified enzymes in biotransformations is rapidly increasing. 

For a review on epoxide hydrolases and related enzymes in the context of organic synthesis, see Faber, K. Biotransformations in Organic Chemistry, Springer New York 2004. 

Biotransformation, in which the main product is formed from substrate through one or more reactions catalysed by enzymes in the cells. Examples steroid hydro xylation. 

German investigators (Brock et al) worked on the creation of alkylating pro-drugs that have cytostatic activity after specific biotransformation in the tumor tissue. Cyclophosphamide (CTX) has well pronounced antitumor activity with the broadest spectrum. It is metabolized to the cytotoxic phosphoamide mustard. In normal tissues with high enzyme level cyclophosphamide is converted to its inactive metabolites (Fig. 2). These differences in biotransformation can explain the relative selectivity of cyclophosphamide towards... 

Reviews see (a) Wong, C.-H. Whitesides, G. M. Enzymes in Synthetic Organic Chemistry, Pergamon Oxford, 1994. (b) Bornscheuer, U. T. Kazlauskas, R. J. Hydrolases in Organic Synthesis Regio- and Stereoselective Biotransformations Wiley Chichester, 1999. 

In the processes that require regeneration of cofactors such as nicotinamide adenine dinucleotide phosphate (NAD(P)H) and adenosine triphosphate (ATP), whole-cell biotransformations are more advantageous than enzymatic systems [12,15]. Whole cells also have a competitive edge over the isolated enzymes in complex conversions involving multiple enzymatic reactions [14]. 

Bioremediation of food industry wastewater Bioremediation is a general concept that includes all those processes and actions that take place as an attempt to biotransform an environment, already altered by contaminants, to its original status. Laccase is a well-known enzyme in bioremediation because of its ability to degrade phenolic compounds (Morozova and others 2007). As mentioned for peroxidase, aromatic compounds, including phenols and aromatic amines, constitute one of the major classes of pollutants and are heavily regulated in many countries. This ability of laccases has been applied in different areas of both the food and textile industries, such as breweries and olive oil factories. 

Romeo, M., A. Mathieu, M. Gnassia-Barelli, A. Romana, and M. Lafaurie. 1994. Heavy metal content and biotransformation enzymes in two fish species from the NW Mediterranean. Afar Ecol. Pmg. Ser. 107 15-22. 

Guengerich, F.P., "Pharmacogenomics of Cytochrome P450 and Other Enzymes Involved in Biotransformation of Xenobiotics," Drug Devel. Res., 49, 4-16 (2000). 

Considerable success has been achieved in isolating plant tissue culture enzymes responsible for specific steps in the biosynthesis of a range of indole alkaloids (187-191). While the subject of biosynthesis is beyond the scope of this review, the value of such enzymes in catalyzing biotransformation reactions... 

For a while, in the early 1990s, the interest in the use of enzymes in organic synthesis increased at an almost exponential rate and two-volume works were needed even to summarize developments in the field151. Now, at the turn of the century, it is abundantly clear that the science of biotransformations has a significant role to play in the area of preparative chemistry however, it is, by no stretch of the imagination, a panacea for the synthetic organic chemist. Nevertheless, biocatalysis is the method of choice for the preparation of some classes of optically active materials. In other cases the employment of man-made catalysts is preferred. In this review, a comparison will be made of the different methods available for the preparation of various classes of chiral compounds161. 

Croci, T. and Williams, G.M. (1985). Activities of several phase I and phase II xenobiotic biotransformation enzymes in cultured hepatocytes from male and female rats. Biochem. Pharm. 17(34) 3029-3035. 

Vrolijk NH, Targett NM (1992) Biotransformation enzymes in Cyphoma gibbosum (Gastropoda, Ovulidae) - implications for detoxification of gorgonian allelochemicals. Mar Ecol Prog Ser... 

With the exception of two dehydrogenases, all of the steroidogenic enzymes belong to the cytochrome P-450 (abbreviated as CYP) family of enzymes. The CYP enzymes are often involved with redox or hydroxylation reactions, and are also found in the liver where they are key players in biotransformation reactions (see Section 6.4). Different members of the CYP family are therefore involved with both synthesis in adrenal and gonads and hepatic inactivation of steroid hormones. 

Considerable interest has developed concerning the nature of the mixed function oxidase system in fish and the role that this system may play in the development of toxic responses in these animals. Studies have shown that components of the mixed function oxidase system are present in relatively high concentrations in fish liver (4, 5, 6) and that the enzyme systems in this organ are capable of many of the biotransformation reactions already described for the mammalian liver (7, 8, 9). The presence of this complement of enzymes in the livers of many fishes suggests that this organ too may be particularly sensitive to insult from sub lethal concentrations of many waterborne toxicants. For this reason, methods to evaluate liver function in fish may be particularly useful in identifying the sublethal effects of certain classes of toxicants. 

Calu-3 cells have shown the ability to perform fatty acid esterification of budes-onide [132], In pre-clinical studies, this esterification results in a prolonged local tissue binding and efficacy, which is not found when the esterification is inhibited [133]. The precise mechanism remains undefined in that the identity of specific enzyme(s) responsible for this metabolic reaction is unclear [134], Assessment of the potential toxicity and metabolism of pharmaceuticals and other xenobiotics using in vitro respiratory models is still at its infancy. The development of robust in vitro human models (i.e., cell lines from human pulmonary origin) has the potential to contribute significantly to better understanding the role of biotransformation enzymes in the bioactivation/detoxication processes in the lung. 

Metabolism of PAHs by the cytochrome P-450-dependent enzymes in fish is a classic deviation from EP theory. When PAH biotransformation product data are available (e.g., concentrations of PAH conjugates or other metabolites in bile). 

In cases where the depuration of HOCs from BMOs involves enzyme-mediated biotransformations (Eq. 7.4) or active transport mechanisms, and environmental concentrations are high (e.g. near a point source), depuration rates have been shown to follow Michaelis-Menten kinetics (Spade and Hamelink, 1985). Michaelis-Menten kinetics is elicited when an enzyme or active transport system is saturated with a chemical. This type of kinetics is characterized by lower values of keS at sites with high HOC concentrations. If k s are unchanged at high concentration sites, Michaelis-Menten kinetics will result in elevated BAFs. However, if chemical concentrations become toxic, finfish likely avoid the area and sessile organisms such as mussels may close their valves for extended periods (Huckins et al., 2004). 

A biological difference that could increase susceptibility of fetuses and premature or perinatal infants to 1,2-dibromoethane toxicity is developmental immaturity of the P-450 (microsomal enzyme) system. Biotransformation of xenobiotics occurs predominantly by glutathione conjugation (Benet and Sheiner 1985 Sipes and Gandolfi 1986). This pathway is known to generate a number of toxic intermediate metabolites of 1,2-dibromoethane. In addition, fetal mice have selective binding of... 

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