Substrate specificity of enzyme

Variations in the substrate specificity of enzymes derived from different sources does occur and cross-reactivity should always be checked when developing an enzymic assay. This includes an investigation of the interference from a variety of substances that may be present in the sample in addition to studies on amino acid specificity. 

Substrate Specificity of Enzymes of Saccharomyces cerevisiae Having a-D-Glucosidase Activity"... 

Almost as impressive as the substrate specificity of enzymes is the specificity for a given type of reaction. Many substrates are capable of undergoing a variety of different chemical reactions, either unimolecular or with water or some other compound present in the cell. The enzyme catalyzes only one of these reactions. 

A. Zaks and A. M. Klibanov, Substrate specificity of enzymes in organic solvents vs. water is reversed,/. Am. Chem. Soc. 1986b, 108, 2767-2768. 

Tomoya Ogawa (Japan) Synthetic approaches to glycan chains 1986—Klaus Bock (Denmark) Carbohydrate-protein interactions. The substrate specificity of enzymes used in the degradation of oligosaccharides related to starch and cellulose... 

This chapter focuses on the creation of novel substrate specificities of enzymes. Although in principle, this would also include altered enantio- or stereoselectivity, this aspect is already covered extensively in Chapter 11. 

Phage libraries have also been used to study the substrate specificity of enzymes by finding an improved artificial substrate. Coombs et al. (69) reported the detailed assessment of specificity for a serine protease belonging to the a-chymotrypsin family, the prostate specific antigen (PSA). They used both substrate optimization by singlepoint mutations and phage display libraries. The sequence of the 14-member substrate 10.2 (70) was used to start the iterative optimization process (Fig. 10.11) in which substitution or exchange of the PI, P2, or P2 residues increased the substrate affinity... 

Developments in molecular biology enable us to change the substrate specificity of enzymes the enzymes can be engineered to be more suitable for the requisite substrate. For example, variations have been made to the structure of the NAD+ dependent L-lactate dehydrogenase from Bacillus stearothermophilus (LDH) 130L Two regions of LDH that border the active site (but are not involved in the catalytic... 

Copolymers containing hydroxyalkanoic acids with a chain length ranging from 3 to 14 carbon atoms have been produced from various carbon substrates (such as sugars, alkanoic acids, alcohols, and alkanes) by a variety of bacteria over 70 strains (Steinbiichel 1991). The PHA compositions produced by a bacterimn are dependent of the substrate specificities of enzymes in the PHA biosynthetic pathway. 

From the great number of oxidoreductases used to modify enzymatic BFC electrodes only a minority is capable of DET, which reduces the number of fuels and oxidants (Table 1). The substrate specificity of enzymes redners half-cell separation by e.g., membranes unnecessary. DET between enzyme and electrode also stops the need for soluble redox mediators to shuttle electrons between enzyme and electrode. This results in the possibility to design membraneless, non-compartmentalized enzymatic BFCs with a simple architecture. However, so far achieved DET currents are lower than MET currents, because usually only enzyme monolayers can be contacted. Strategies to improve the current density aim at the use of high surface area electrode materials like CNTs, AuNPs etc. or the layer-by-layer approach... 

It appears, from the preceeding paragraph, that in mammals as well as in bacteria there must be a mechanism for the production of at least some amines. The route is now known to be formally the same as that in bacteria, i.e. decarboxylation of amino acids, but a distinction must be made between the bacterial and mammalian enzymes, not only on the grounds of differences in the physiological function of the products, but also because of differences in the substrate specificities of enzymes from the two sources. 

The substrate specificity of enzymes shows the following differences. The occurrence of a distinct functional group in the substrate is the only prerequisite for a few enzymes, such as some hydrolases. This is exenqtlified by nonspecific lipases (cf. Table 3.21) or peptidases (cf. 1.4.5.2.1) which generally act on an ester or peptide covalent bond. 

Arene dioxygenases catalyze the first step in the metabolism of unactivated aromatic compounds, yielding cw-dihydrodiol of aromatics. As shown in eq. (22), the reaction requires nicotinamide adenine nucleotide (NADH) and molecular oxygen. Substrate specificity of enzymes is high, and products shown in Fig. 27 are produced by benzene-[351, 352], toluene- [353-356], naphthalene- [357-361], biphenyl- [362-364], benzoate-[365-370], and phthalate-dioxygenases [371-378]. In the cases of benzoate [379], 4-sulphobenzoate [380], and 6>-nitrotoluene [381], catechols are formed via unstable dihydroxylated intermediates as shown in eq. (23)... 

Various examples were described, including whole cell-biocatalyzed reductions [4], especially employing baker s yeast [la,5]. However, there was always the problem that several active enzymes with different selectivities were present, although in particular cases excellent conversions and stereoselectivities were achieved. Later on, by directed evolution techniques [6], improvement of stereoselectivities and substrate specificities of enzymes was achieved, as well as several enzymatic properties (e.g., thermal stability) were modified. Moreover, large amounts of biocatalysts have been produced by fermentation of recombinant bacteria that express the gene, when their corresponding DNA has been doned. The drawback of the expensive cofactor recyding has also been overcome by the devdopment of effident techniques [7]. 

The correlation was unexpectedly high as seen in Figure 13.4.3.2, implying that the change of substrate specificity of enzyme in organic solvent stems to a large extent from the energy of desolvation of the substrate. 

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