Enzymes classes

Reactions can also be searched by enzymes, either by enzyme name or enzyme class (EC notation), both in specific or in generic form. Table 10.3-1 shows the results of searching for EC classes. 

In order to broaden the field of biocatalysis in ionic liquids, other enzyme classes have also been screened. Of special interest are oxidoreductases for the enan-tioselective reduction of prochiral ketones [40]. Formate dehydrogenase from Candida boidinii was found to be stable and active in mixtures of [MMIM][MeS04] with buffer (Entry 12) [41]. So far, however, we have not been able to find an alcohol dehydrogenase that is active in the presence of ionic liquids in order to make use of another advantage of ionic liquids that they increase the solubility of hydrophobic compounds in aqueous systems. On addition of 40 % v/v of [MMIM][MeS04] to water, for example, the solubility of acetophenone is increased from 20 mmol to 200 mmol L ... 

Beside AAC enzymes two different enzyme classes, nucleotidyltransferases (ANT enzymes), and phosphotransferases (APH enzymes) modify the hydroxyl groups of aminocyclitol-aminoglycoside antibiotics. 

ET-1 from big-ET-1 by other proteases such as neutral endopeptidase or other currently unidentified proteases. Therefore, dual inhibition of ECE and NEP might inhibit ET-l generation more efficiently, than that seen for selective ECE inhibitors. However, dual inhibiton of ECE and NEP could also increase the risk for the development of AD, as both enzyme classes are involved in the degradation of A 3 peptide. 

In vanadium-dependent haloperoxidases, the metal center is coordinated to the imidazole system of a histidine residue, which is similarly responsible for creating hypochlorite or hypobromite as electrophilic halogenating species [274]. Remarkably, a representative of this enzyme class is capable of performing stereoselective incorporation of halides, as has been reported for the conversion of nerolidol to various snyderols. The overall reaction commences through a bromonium intermediate, which cyclizes in an intramolecular process the resulting carbocation can ultimately be trapped upon elimination to three snyderols (Scheme 9.37) [275]. 

All the transformations described above may be realized using various classes of enzymes. However, the importance for practical applications in organic synthesis is not the same for each class of the six enzyme classes, two are most commonly used hydrolases and oxidoreductases (altogether >85% of the total applications) [1, 3]. 

Examples of such systems include the reactions of kinases, phosphatases, hydroxylases, acetylases, ubiquitin transferases, and many other enzyme classes that represent attractive targets for drug discovery. There are several mechanisms by which an enzyme can catalyze these types of reactions, and the details of the mechanism are important in determining the best approach to designing activity assays for the enzyme and for proper evaluation of inhibitors that are identified through those activity assays. 

Table 1 summarizes the international classification of enzymes. Classes EC1 and EC3 are the most widely used for the development of optical biosensors. Sometimes different enzymes and transducing schemes can be applied to the analysis of a single analyte and the best combination should be selected depending on the application. 

The fact that enzymes also work in organic solvents [42], ranging from apolar alkanes up to the very polar N,N-dimethylformamide [65], has (Fig. 13.10) and will continue to open up new cascade opportunities for the integration of enzymatic conversions with chemocatalytic methods that require organic solvents. Notably, however, some enzyme classes, for instance the carbohydrate-converting enzymes, do not show activity in non-aqueous media [40, 41]. 

Hoemann, K. and Bucher, P. The UBA domain a sequence motif present in multiple enzyme classes of the ubiquitmation pathway. Trends Biochem. Sci. 1996, 21, 172—73. 

No attempt has been made to cover all drug classes or enzyme classes instead, a flavour of the potential benefits that can be achieved by the adoption of biocatalytic methods as a compliment to chemical approaches is given. Biocatalytic methods of accessing chiral building blocks will only occasionally be discussed here and the reader is referred to a number of comprehensive reviews that have been published elsewhere. 

It should be noted that some commercial enzyme preparations may contain several enzyme isomers (enzymes derived from one source which belong to the same enzyme class but differ in specificity, stability or other properties). This is most often the case when the commercial preparation was developed for a process industry application rather than a specific chemical biotransformation application. Some fungal enzymes, such as laccase, are sometimes supplied as crude enzyme mixtures. Fungal laccases are manufactured on a huge scale (multitonne per annum) and are principally used in bulk processes such as wood... 

Organism and functional state of the enzyme Class Method Res. (nm) Reference Year PDB ... 

In both cases the metal ion closest to the Fe-S cluster is being reduced. Hence, the mechanism of H2 oxidation may be very similar for the two enzyme classes. The main change in the CO region of the FTIR spectrum during the reduction of the D. vulgaris... 

In this reaction, one molecule of ribulose-1,5-bisphosphate (metabolite 1) and one molecule of CO2 (metabolite 2) give rise to two molecules of 3-phosphoglycerate (metabolite 3). The enzyme responsible has the EC number 4.1.1.39. The annotated enzyme list shows that this refers to ribulose bisphosphate carboxylase ( rubisco for short). Rubisco belongs to enzyme class 4 (the lyases) and, within that group, to subclass 4.1 (the car-boxy-lyases). It contains copper as a cofactor ([Cu]). 

The enzyme class of transferases is subdivided into nine subclasses ... 

Originally almost all apphcations of biocatalysis involved hydrolytic reactions, except a few, such as L-sorbose and ephedrine manufacture (Turner, 1994). Hydrolases still are the main conunercial enzyme class, but nowadays a much wider range of reactions is being applied, either on a conunercial scale or on a lab scale. The most important reaction types are reviewed in chapter 2. 

The lyases comprise enzyme class 4. They are enzymes cleaving C-C, C-0, C-N and other bonds by elimination, not by hydrolysis or oxidation. Lyases also catalyse addition to donble bonds. The types of reactions catalysed by lyases are decarboxylation (decarboxylase), hydration/dehydration (hydratase/dehydratase), ammonia addition/deamination (ammonia-lyase), cyanohydrin formation/cleavage (oxynitrilase),... 

The isomerases comprise enzyme class 5 and they are enzymes catalyzing changes within one molecule. Important subclasses are racemaces and epimerases (EC 5.1) and intramolecular oxidoreductases (EC 5.3). 

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