Characteristics of Enzymes

Some nucleic acids are capable of self-splicing. These catalytic DNA and RNA are known as deoxyribozymes (Li and Breaker, 1999 Sheppard et al, 2000) and ribozymes (Doherty and Doudna, 2000 Scott and Klug, 1996) respectively. The 3 - and/or 2 -hydroxyls of DNA/RNA serve as a catalytic site that invariably requires a metal ion for the catalytic activity. Deoxyribozymes are quasi-catalytic while ribozymes can be catalytic, e.g. ribonuclease P (RNase P) as well as quasi-catalytic, e.g. introns and hammerhead RNAs. RNase P resources are maintained at http //www.mbio.ncsu.edu/RnaseP/homeJitml 

Supramolecular aspects of enzymes , in Comprehensive Supramolecular Chemistry, J.L. Atwood, 

Enzymes are of vital importance and interest in biochemistry. It is enzymes that catalyse essentially all biological processes and, as we will see in Chapter 12, they have stimulated a wealth of interest from supramolecular chemists. Enzymes are dynamic macromolecules with a molecular weight 

EC 2 Transferases transfer a fnnctional gronp (e.g. a methyl or phosphate group) 

EC 4 Lyases cleave varions bonds by means other than hydrolysis and oxidation 

EC 5 Isomerases catalyze isomerisation changes within a single molecnle 

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The biological dehydrogenation of succinic acid described in Section 5 8 is 100% stereoselective Only fumaric acid which has a trans double bond is formed High levels of stereoselectivity are characteristic of enzyme catalyzed reactions... 

The characteristics of enzymes are their catalytic efficiency and their specificity. Enzymes increase the reaction velocities by factors of at least one million compared to the uncatalyzed reaction. Enzymes are highly specific, and consequendy a vast number exist. An enzyme usually catalyzes only one reaction involving only certain substrates. For instance, most enzymes acting on carbohydrates are so specific that even the slightest change in the stereochemical configuration is sufficient to make the enzyme incompatible and unable to effect hydrolysis. 

Another characteristic of enzymes is their frequent need for cofactors. A cofactor is a nonproteia compound that combines with the otherwise iaactive enzyme to give the active enzyme. Examples of cofactors are metal ions such as Ca ", Cu ", Co ", Fe ", and and organic molecules such as... 

Various chemical species influence the rates of hydrolysis of penicillins, e.g. metal ions (Cu >Zn >Ni Co ) (80JCS(P2)1725), carbohydrates (78MI51101), certain amine-containing catechol derivatives (69JPS1102) and /3-cyclodextrin (71JA767). Some of these even show some of the characteristics of enzyme-catalyzed hydrolyses. 

Maltose phosphorylase proceeds via a single-displacement reaction that necessarily requires the formation of a ternary maltose E Pi (or glucose E glucose-l-phosphate) complex for any reaction to occur. Exchange reactions are a characteristic of enzymes that obey double-displacement mechanisms at some point in their catalysis. 

The response characteristics of enzyme electrodes depend on many variables, and an understanding of the theoretical basis of their function would help to improve their performance. Enzymatic reactions involving a single substrate can be formulated in a general way as... 

Enzymes are proteins catalyzing all in vivo biological reactions. Enzymatic catalysis can also be utilized for in vitro reactions of not only natural substrates but some unnatural ones. Typical characteristics of enzyme catalysis are high catalytic activity, large rate acceleration of reactions under mild reaction conditions, high selectivities of substrates and reaction modes, and no formation of byproducts, in comparison with those of chemical catalysts. In the field of organic synthetic chemistry, enzymes have been powerful catalysts for stereo- and regioselective reactions to produce useful intermediates and end-products such as medicines and liquid crystals. ... 

Cyclodextrins as catalysts and enzyme models It has long been known that cyclodextrins may act as elementary models for the catalytic behaviour of enzymes (Breslow, 1971). These hosts, with the assistance of their hydroxyl functions, may exhibit guest specificity, competitive inhibition, and Michaelis-Menten-type kinetics. All these are characteristics of enzyme-catalyzed reactions. 

Enzymes are remarkable molecular devices that determine the pattern of chemical transformations in biological systems. The most striking characteristics of enzymes are their catalytic power and specificity. As a class of macromolecules, they are highly effective in catalyzing diverse chemical reactions because of their ability to specifically bind to a substrate and their ability to accelerate reactions by several orders of magnitude. Applying enzymes or organisms in... 

There are three characteristics of enzymes that form the basis of most of their properties the active site, the enzyme-substrate complex and the transition state. 

Also characteristic of enzymes that obey Michaelis-Menten kinetics is that suitable inhibitors can compete with the substrate for the enzyme active site, thus impeding the reaction. If the inhibitor binds reversibly to the enzyme active site, then the substrate can compete for the active site leading to competitive inhibition. To test for... 

Antonova, T., Nachev, L., Kosturkova, P., Daov, T. and Dedova, R 1978. Study of bacterial strains producing milk-coagulating enzymes. VII. Characteristics of enzyme complex produced after different fermentation times. Acta Microbiol. Bulg. 1, 21 — 29. 

The outstanding characteristic of enzyme catalysis is that the enzyme specifically binds its substrates, with the reactions taking place in the confines of... 

Inhibitors are substances that tend to decrease the rate of an enzyme-catalysed reaction. Although some act on the substrate, the discussion here will be restricted to those inhibitors which combine directly with the enzyme. Inhibitors have many uses, not only in the determination of the characteristics of enzymes, but also in aiding research into metabolic pathways where an inhibited enzyme will allow metabolites to build up so that they are present in detectable levels. Another important use is in the control of infection where drugs such as sulphanilamides competitively inhibit the synthesis of tetrahydrofolates which are vitamins essential to the growth of some bacteria. Many antibiotics are inhibitors of bacterial protein synthesis (e.g. tetracyclin) and cell-wall synthesis (e.g. penicillin). 

Enzymes are biocatalysts, as such they facilitate rates of biochemical reactions. Some of the important characteristics of enzymes are summarized. Enzyme kinetics is a detailed stepwise study of enzyme catalysis as affected by enzyme concentration, substrate concentrations, and environmental factors such as temperature, pH, and so on. Two general approaches to treat initial rate enzyme kinetics, quasi-equilibrium and steady-state, are discussed. Cleland s nomenclature is presented. Computer search for enzyme data via the Internet and analysis of kinetic data with Leonora are described. 

Enzymes are globular proteins whose sole function is to catalyze biochemical reactions. The most important properties of all enzymes are their catalytic power, specificity, and capacity to regulation. The characteristics of enzymes (Copeland, 2000 Fersht, 1985 Kuby, 1991 Price and Stevens, 2000) can be summarized as follows ... 

The argument previously outlined provides an appealing physiochemi-cal explanation for the stability and activity behavior of homologous enzymes adapted to different temperatures. However, one cannot interpret the behavior of a biological system solely in physiochemical terms. All these enzymes are the products of evolution. While they are certainly subject to the laws of physics and chemistry, the evolutionary process imposes its own, additional constraints. We will see that the stability-activity trade-off is not a necessary characteristic of enzymes, especially not those evolved in the laboratory. 

Kooreman, J.A., Physical and Chemical Characteristics of Enzyme Converted Syrup, Manufacturing Confectioner, June, 35-90 (1955). 

Parkin, K.L. 1993. General characteristics of enzymes. In Enzymes in food processing, ed. T. Nagodawithana and G. Reed. San Diego, CA Academic Press, Inc. 

The characteristics of enzymes as catalysts may be represented by high spedfidty, high efficiency, and the regulatory function. Althou all of these characteristics should be the target for pdymer catalysts separately or in combination, some progress has only been made with regard to hydrolytic efficiency. 

In this section, neral characteristics of enzyme catalysis are briefly mentioned and then the functions of chymotrypsin and lyso me are discussed as two specifk exanqdes of the hydrolytic mzyme. 

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