Specificity, of enzymes

Emulsin does not hydrolyse a-methylglucoside, whereas it readily hydrolyses -methylglucoside, salicin, amygdalin and arbutin. This is an excellent example of the specificity of enzymes ... 

The specificity of enzyme reactions can be altered by varying the solvent system. For example, the addition of water-miscible organic co-solvents may improve the selectivity of hydrolase enzymes. Medium engineering is also important for synthetic reactions performed in pure organic solvents. In such cases, the selectivity of the reaction may depend on the organic solvent used. In non-aqueous solvents, hydrolytic enzymes catalyse the reverse reaction, ie the synthesis of esters and amides. The problem here is the low activity (catalytic power) of many hydrolases in organic solvents, and the unpredictable effects of the amount of water and type of solvent on the rate and selectivity. 

Conformationally restricted analogs of substrates can be useful in elucidating both the substrate specificities and the product specificities of enzymes. The restriction can help stabilize an intermediate in the enzymatic process so that it may be isolated. Two or more otherwise structurally equivalent portions of a substrate may be rendered nonequivalent by the restriction so that potential differentiation of these portions by the enzyme in determining product specificity may be investigated. 

Early in the last century, Emil Fischer compared the highly specific fit between enzymes and their substrates to that of a lock and its key. While the lock and key model accounted for the exquisite specificity of enzyme-substrate interactions, the imphed rigidity of the... 

While many diseases have long been known to result from alterations in an individual s DNA, tools for the detection of genetic mutations have only recently become widely available. These techniques rely upon the catalytic efficiency and specificity of enzyme catalysts. For example, the polymerase chain reaction (PCR) relies upon the ability of enzymes to serve as catalytic amplifiers to analyze the DNA present in biologic and forensic samples. In the PCR technique, a thermostable DNA polymerase, directed by appropriate oligonucleotide primers, produces thousands of copies of a sample of DNA that was present initially at levels too low for direct detection. 

With regard to the specificity of enzymes, there are four main types ... 

By means of genetic engineering, including cloning and site-directed mutagenesis, it has become possible for modern synthetic chemists to utilize a sufficient amount of isolated enzyme catalysts and to modify the reactivity, stability, or even specificity of enzymes. Therefore, polymerizations catalyzed by isolated enzyme are expected to create a new area of precision polymer syntheses. Furthermore, enzymatic polymerizations have great potential as an environmentally friendly synthetic process of polymeric materials. 

The action pattern and the specificity of enzymes acting on homo-polymeric substrates are determined by the nature of the active center.134-137 Hence, it may be assumed that the active centers of enzymes exhibiting the aforementioned action-patterns are different. 

Some model complexes in the reaction with diribonucleotides or cyclic ribonucleotides show remarkable substrate and regioselectivity and thus mimic the specifity of enzymes in these respects. 

As already stated, Fischer was deeply intrigued by the phenomenon of enzyme activity. He realized that the substances were proteins and this undoubtedly was why he next undertook the study of amino acids and peptides. He fully appreciated that the specificity of enzyme catalysis depended on the occurrence of a complementarity for interacting dissymmetric surfaces. In this regard, he wrote (3) ... 

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. 

The immense catalytic power of enzymes means that a compound, even at a very low concentration, can rapidly be converted to a product whose concentration can then be measured by a sensitive technique. The specificity of enzymes ensures that they react with only one compound, even in the presence of many other similar compounds. This property can be used, for example, in measuring the concentration of glucose in body fluids. 

Aconitase was first described 50 years ago by Martius (1,2) and soon there after named by Breusch (3). The enzyme demonstrated the then surprizing ability to distinguish between the chemicadly identical acetyl arms of citrate (4). The stereo-specificity of enzyme catalyzed reactions was not fully understood until the late 1940 s when Ogston point out that as long as a substrate attaches to an asymmetric enzyme at three points, the enzyme can differentiate between two identical amis of a symmetrical molecule (5). 

Immunological assays measure those moieties that can cause an antigenic response. For the most part, immunological assays should not be interfered with by antibiotics from the other antibiotic families, the specificity of the antibodies being vaguely similar to the specificity of enzyme systems. 

The catalytic efficiency and exquisite specificity of enzymes have been exploited for use as therapeutic agents in certain diseases. 

In general, the high specificity of enzymes limits the application of this method, because for the treatment of each wastewater sample it is necessary to use a special consortium of various types of enzymes. Therefore, for practical reasons the acid hydrolysis of wastewater is the preferred laboratory method for the pretreatment of polymers. By the use of acid hydrolysis for one hour at 148°C with 6 mol/1 HCl ( acid hydrolyse kit from Dr. Lange GmbH Berlin 1996 [48]), the polymers are decomposed to their monomers such as monosaccharides, glycerol, fatty acids, or amino acids, respectively. The hydrolysis of wastewater caused in most cases an increase of the BOD measured (Table 6), resulting in an improved concurrence of sensorBOD and BOD5 [53,68]. 

As discussed in part 2.3.4 choice of acyl donor in transesterifications may have significant influence. The specificity of enzymes may also be influenced by the water activity, a. There are reports showing both positive and negative reports on E. Since water is introduced in the medium other equilibria are established such as between the acyl donor and water and between the produced ester and water, both leading to the formation of acid in the system. How this influences the reaction is not clear. 

Similar explanations, supported by convincing evidence, have been proposed for the high catalytic efficiency and specificity of enzymes (particularly hydrolytic enzymes) relative to ordinary catalysts (Laidler, 23, Wilson, 65, 66). 

Problem 21.51 Account for the stereochemical specificity of enzymes with chiral substrates. 

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