Chemical reactions enzyme-catalyzed

Enzymes, in general, provide speed, specificity, and regulatory control to reactions in the body. Enzymes are usually proteins that act as catalysts, compounds that increase the rate of chemical reactions. Enzyme-catalyzed reactions have three basic steps ... 

Contrary to common chemical reactions, enzyme-catalyzed reactions as well as growth of microorganisms show a so-called temperature optimum, which is a temperature-dependent maximum resulting from the overlapping of two counter effects with significantly different activation energies (cf. 2.5.4.2) ... 

Optically inactive starting materials can give optically active products only if they are treated with an optically active reagent or if the reaction is catalyzed by an optically active substance The best examples are found m biochemical processes Most bio chemical reactions are catalyzed by enzymes Enzymes are chiral and enantiomerically homogeneous they provide an asymmetric environment m which chemical reaction can take place Ordinarily enzyme catalyzed reactions occur with such a high level of stereo selectivity that one enantiomer of a substance is formed exclusively even when the sub strate is achiral The enzyme fumarase for example catalyzes hydration of the double bond of fumaric acid to malic acid m apples and other fruits Only the S enantiomer of malic acid is formed m this reaction... 

Pisakiewicz, D. Kinetics of Chemical and Enzyme-Catalyzed Reactions. Oxford University Press New York, 1977. 

Enzyme kinetics is studied for two reasons (1) it is a practical concern to determine the activity of the enzyme under different conditions (2) frequently the analysis of enzyme kinetics gives information about the mechanism of enzyme action. Chapter 7, Enzyme Kinetics, begins with an introductory section on the discovery of enzymes, basic enzyme terminology and a description of the six main classes of enzymes and the reactions they catalyze. The remainder of the chapter deals with basic aspects of chemical kinetics, enzyme-catalyzed reactions and various factors that affect the kinetics. 

The catalytic ability of enzymes is due to its particular protein structure. A specific chemical reaction is catalyzed at a small portion of the surface of an enzyme, which is known as the active site. Some physical and chemical interactions occur at this site to catalyze a certain chemical reaction for a certain enzyme. 

Enzymes as catalysts Enzymes are catalysts that increase the rate of a chemical reaction without being changed themselves in the process. In the absence of an enzyme, the reaction may hardly proceed at all, whereas in its presence the rate can be increased up to 107-fold. Enzyme catalyzed reactions usually take place under relatively mild conditions (temperatures well below 100°C, atmospheric pressure and neutral pH) as compared to the corresponding chemical reactions. Enzymes are also highly specific with respect to the substrates that they act on and the products that they form. In addition, enzyme activity can be regulated, varying in response to the concentration of substrates or other molecules (see Topic C5). Nearly all enzymes are proteins, although a few catalytically active RNA molecules have been identified. 

Life is sustained by a complex network of chemical reactions. Enzymes, the molecules that catalyze chemical reactions in biological systems, are one of the most remarkable class of molecules generated by evolution. Their performances, typically, far exceed those of man-made catalysts. Being able to accelerate reactions by up to 10 -fold relative to the uncatalyzed reaction [1], they allow reactions which would have half-lives of tens of millions of years to occur in milliseconds. Furthermore, catalysis typically occurs at ambient temperature and neutral pH, and is frequently exquisitely regio- and stereo-selective. 

Enzymes serve as catalysts by decreasing the free energy of activation of chemical reactions. Enzymes accelerate reactions by providing a reaction pathway in which the transition state (the highest-energy species) has a lower free energy and hence is more rapidly formed than in the un -catalyzed reaction. 

In the early days of biochemistry, enzymes were named at the whim of their discoverers. Often enzyme names provided no clue to their function (e.g., trypsin), or several names were used for the same enzyme. Enzymes were often named by adding the suffix -ase to the name of the substrate. For example, urease catalyzes the hydrolysis of urea. To eliminate confusion, the International Union of Biochemistry (IUB) instituted a systematic naming scheme for enzymes. Each enzyme is now classified and named according to the type of chemical reaction it catalyzes. In this scheme an enzyme is assigned a four-number classification and a two-part name called a systematic name. In addition, a shorter version of... 

Age does not seem to alter the pharmacokinetics. Tests in patients with genetic deficiency of pseudocholinesterase also showed no significant difference in tm. The half-life of succinylcholine, on the other hand, increased from 2.6 minutes to 4 hours in patients devoid of this enzyme. It appears that the ester group activation of the Hofmann elimination reaction mutually promotes ester hydrolysis as well. The goal of chemical- over enzyme-catalyzed metabolism in vivo seems to have been achieved. The possibility that ester hydrolysis may be catalyzed by nonspecific esterases is likely that plasma cholinesterase is not utilized is established. 

On the chemical level, enzyme-catalyzed recycling of substrates/coenzymes to improve sensitivity of an assay has been successfully demonstrated [27, 38, 39]. The principle is illustrated in the reaction sequence shown in figure 22.5. 

Much has been done, said, and written in enzyme kinetics and I will mention only a few things. The enzymes are usually selective they catalyze only a single reaction or only one type of reaction. While enzymes generally speed up the reactions, in comparison to the same reaction conducted in the laboratory, the enzymes that are not very selective are usually relatively slow. On the other hand, certain highly selective enzymes, like carbonic anhydrase or glutamate mutase, can speed up the reaction conducted under laboratory conditions by a factor of 10 -lO, that is, trillion-to quadrillion-fold. No man-made catalyst matches this efficiency. Thousands of enzymes are known today they are catalogued into six major categories, in relation to the type of chemical reaction they catalyze. Each enzyme is identified by its enzyme code number, or E.C. number [5]. 

Substrates or products of the TK reaction cannot be specifically quantified by any molecular property, which requires a subsequent specific chemical or enzyme-catalyzed cascade reaction to create a measurable signal for specific quantification. Such coupled assays can be classified according to the nature of the auxiliary agent involved in the cascade reaction. Depending on the principle of the assay, continuous measurements or only discontinuous end-point determinations can be made. 

Unlike chemical reactions, enzyme and microbial reactions are generally complex. The mechanism of enzyme catalyzed reactions is discussed in the next basic operation. ... 

All detergent enzymes are classified as hydrolases due to the chemical reactions they catalyze—the addition of water to the substrate which breaks a covalent chemical bond. The hydrolysis bond-breaking reactions are illustrated in Fig. 3. 

Scientific Background The Source of Enzymes.195 In the living world, each chemical reaction is catalyzed by its own... 

In cellular biological organisms nearly all chemical reactions are catalyzed by enzymes. For example, the enzyme urease catalyzes the hydrolysis of urea and the enzyme protease catalyzes the hydrolysis of proteins. Most enzymes are proteins, although some ribonucleic acids have been found to exhibit catalytic activity and have been called ribozymes. Ribozymes usually catalyze the combination of other RNA fragments, and require the presence of divalent metal ions such as Mg +. It has been thought that divalent metal ions were necessary to the function of ribozymes, but... 

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