Specificity regiospecificity

The specificity of biocatalysts also extends to site specificity (regiospecificity). This means that if several functional groups of one type are present on the molecule, only one specific position will be affected. An example of this is the microbial oxidation of D-soibitol to L-soibose, a key step in the synthesis of vitamin C (Figure 2.4). 

The enzymatic transformation of natural products is by for file most attractive option. In this approach, it can be envisaged that sterols, which are relatively abundant, may be selectively modified to produce desired products. Hie diversity of enzyme activities, their reaction specificity, regiospecificity and stereospedfidty are all features which could contribute to carrying out the desired changes. This does not mean, however, that transformations using enzyme systems are simple. Nevertheless, biotransformations have become of vital importance in the production of steroids. 

Itoh N, AKM Quamrul Hasan, Y Izumi, H Yamada (1988) Substrate specificity, regiospecificity and stereospecificity of halogenation reactions catalyzed by non-heme-type bromoperoxidase of Corallina pilulifera. Eur J Biochem 172 477-484. 

Specificity of lipases may be expressed in a number of different ways—substrate specific, regiospecific, nonspecific, fatty acyl specific, and stereospecific. Examples of these specificities have been presented by Villeneuve and Foglia (1997) (Table 10-6). 

Specificity is one of the most striking properties of enzyme molecules. Enzyme specificity can be defined as a comparative difference in rates of catalysis of certain reactions. After an enzyme is identified as a hpase, several specificities within the class are identified or can be expected to occur. The main advantage of lipases, which differentiate enzymatic reactions from chemically-catalyzed reactions, is lipase specificity. Lipases have turned out to be very useful enzymes for catalyzing various types of reactions with a rather wide substrate specificity. The fatty acid specificity of lipases has been exploited to produce structured lipids and to enrich lipids with specific fatty acids to improve the nutritional characteristics of lipids (24). Certain lipases display positional specificity (regiospecificity) toward fatty acyl groups in a TAG molecule as well as fatty acid selectivity. 

Lipases can be categorized into three groups based on their specificity random (nonregiospecific), in-1,3-specific (regiospecific) toward TAGs, or specific for a particular fatty acid or, more generally, a class of fatty acids (Figure 10). Examples... 

The examples above represent some of the most successful studies in protein engineering. They show that it is possible to enhance protein thermostability rationally, alter cofactor or substrate specificity, regiospecificity, and even change catalytic activity. Furtherm ore, the creation of enzymatic activity from a non-catalytic protein backbone, and the creation of a biocatalyst with an unprecedented catalytic activity not found in nature, have also been achieved. However, the examples published in the literature are probably only a tiny fraction of the many studies that have been, or are still, in progress awaiting positive results. 

Matsunaga I, Sumimoto T, Ueda A, Kusunose E, Ichihara K (2000) Fatty acid-specific, regiospecific, and stereospecific hydroxylation by cytochrome P450 (CYP152B1) fiom Sphingomonas paucimobi-lis substrate structure required for alpha-hydroxyl-ation. Lipids 35 365 371... 

Possible control of substrate specificity, regiospecificity, and enantioselec-tivity. 

It has been recognized that an enzyme has three levels of specificity structural specificity, regiospecificity, and stereospecificity. An enzyme must first recognize some common structural features on a substrate (and a coenzyme) to produce a specific catalysis. Second, catalysis must occur at a specific region on the substrate (or the coenzyme) and the stereochemical outcome must be controlled by the enzyme. 

With MMA, these radicals show a quite different order of specificity regiospecificity decreases in the series cyanoisopropyl methyl > phenyl > benzoyloxy > t-butoxy. Cyanoisopropyl... 

Ester, ether, and cycHc acetal groups are used as blocking groups to allow regiospecific reactions to take place, ie, reaction at specific unblocked hydroxyl groups. 

Look carefully at the reactions shown in the previous section. In each case, an unsymmetrically substituted alkene has given a single addition product, rather than the mixture that might have been expected. As another example, 1-pentene might react with HC1 to give both 1-chloropentane and 2-chloropentane, but it doesn t. Instead, the reaction gives only 2-chloropentane as the sole product. We say that such reactions are regiospecific (ree-jee-oh-specific) when only one of two possible orientations of addition occurs. 

Regiospecific (Section 6.8) A term describing a reaction that occurs with a specific regiochemistry to give a single product rather than a mixture of products. 

Stereosperificity Regiospecificity Reaction specificity Reduced disposal costs... 

In short, the space within the active site and the orientation of the substrate are both important determinants for the positional specificity of plant LOXs and are modified by additional factors such as substrate concentration, the physicochemical state of the substrate, pH, or temperature (Lopez-Nicolas and others 2000). However, it should be stressed that for other LOXs regiospecificity may be determined in a more complex manner. 

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