Enzyme Classification and Examples

In all three examples, / -elimination was monitored by measuring the absorbance at 235 nm (with high-molecular substrates). Voragen186 pointed out that use of these substrates, which, at higher concentrations, can form viscous, optically dense solutions, could prevent the measurement of absorbance at 235 nm and thus cause an error in enzyme classification. The existence of polymethylgalacturonase is not definite, and revision of some of the results may be necessary. 

The use of enzymes and whole cells as catalysts in organic chemistry is described. Emphasis is put on the chemical reactions and the importance of providing enantiopure synthons. In particular kinetics of resolution is in focus. Among the topics covered are enzyme classification, structure and mechanism of action of enzymes. Examples are given on the use of hydrolytic enzymes such as esterases, proteases, lipases, epoxide hydrolases, acylases and amidases both in aqueous and low-water media. Reductions and oxidations are treated both using whole cells and pure enzymes. Moreover, use of enzymes in sngar chemistiy and to prodnce amino acids and peptides are discnssed. 

This classification is perfectly valid for the metalloenzymes, even though most of them fall in group 1, such as the several dioxygenases, (mono)oxygen-ases, and oxidases (dehydrogenase). Many examples will be discussed in the later chapters of the book. The enzymes known and classified [7] so far very often involve a metal, either directly at the active center or indirectly at another place, for instance, in the electron transfer process [8],... 

The International Union of Biochemistry has recommended that enzymes have three names, namely a systematic name, which shows the reaction being catalysed and the type of reaction based on the classification in Table A7.1, a recommended trivial name and a four figure Enzyme Commission code (EC code). Nearly all systematic and trivial enzyme names have the suffix -ase. Systematic names show, often in semi-chemical equation form, the conversion the enzyme promotes and the class of the enzyme. Trivial names are usually based on the function of the enzyme but may also include or be based on the name of the substrate. However, some trivial names in current use are historical and bear no relationship to the action of the enzyme or its substrate, for example, pepsin and trypsin are the names commonly used for two enzymes that catalyse the breakdown of proteins during digestion. The Enzyme Commission s code is unique for each enzyme. It is based on the classification in Table A7.1 but further subdivides each class of enzyme according to how it functions. The full code is... 

The names of the examples of textile-relevant enzymes follow the nomenclature of Duclaux from 1898, characterising an enzyme by the end-syllable ase , added to the name of the snbstrate that is split, synthesised or otherwise catalysed. As with all catalysts, enzymes reduce the activation energy of a specific reaction. The discovery of large qnantities of new enzyme systems afforded a more differentiated nomenclatnre, realised in 1964 by the International Union of Pure and Applied Chemistry (lUPAC) and the International Union for Biochemistry (lUB). In the new enzyme classification (EC) the first nnmber refers to one of the six main gronps and the following numbers to subgroups, for example EC 3.4.S.6, where 3 stands for hydrolases. ... 

The systematic name of an enzyme consists of two parts, the first originating from the equation, the second from the type of reaction catalyzed. In addition, according to the recommendations of the International Union of Pure and Applied Chemistry and the International Union of Biochemistry (1973), each enzyme bears a number from the international EC (Enzyme Classification) system, which reflects the main class, the subclass, and the subgroup. The number is completed by a special enzyme number. Thus, for example the EC number 1.1.3.4 of the enzyme with the trivial name glucose oxidase results from the following ... 

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... 

The widely accepted basis of all enzyme classifications are the recommendations of the Enzyme Committee (E.C.) of the International Union of Biochemistry and Molecular Biology (IUBMB)1491. Within this system, enzymatic activities are classified by a four-level hierarchy and each entry is described by a set of four numbers. The first number describes the top level and can be either 1 for oxidoreductases, 2 for transferases, 3 for hydrolases, 4 for lyases, 5 for isomerases or 6 for ligases. The meaning of the three lower hierarchy levels depends on the top level group. As an example, glycogen synthase is classified as 2.4.1.11 here, the 2 stands for transferases, the 4 for glycosyl-transferases, the 1 for hexosyl-transferases and the 11 for the particular subfamily. 

As shown in I Table 12.4, the functions of minerals are consistent with their classification as major or trace and with the amount required daily in the diet. For example, compounds of some major minerals (Ca and P) are the primary inorganic structural components of bones and teeth. Other major minerals (Na, K, Cl, and Mg) form principal ions that are distributed throughout the body s various fluids. Some trace minerals are components of vitamins (Co), enzymes (Zn and Se), hormones (I), or specialized proteins (Fe and Cu). Thus, we see that even though trace minerals are required in small quantities, their involvement in critical enzymes, hormones, and the like makes them equally as important for good health as the major minerals. 

Tab. 1 International classification of enzymes, and examples for enzymes employed in electrochemical biosensors... 

Chapter 2 covers the basic principles of chemical kinetics and catalysis and gives a brief introduction on classification and types of chemical reactors. Differential and integral methods of analysis of rate equations for different types of reactions—irreversible and reversible reactions, autocatalytic reactions, elementary and non-elementary reactions, and series and parallel reactions are discussed in detail. Development of rate equations for solid catalysed reactions and enzyme catalysed biochemical reactions are presented. Methods for estimation of kinetic parameters from batch reactor data are explained with a number of illustrative examples and solved problems. 

Until very recently the naming of the individual enzymes has been entrusted largely to the discoverers. This resulted often in such descriptive names as zwisch-enferment or pH 5 enzyme. An international commission meanwhile has drafted specific rules for the classification and nomenclature of enzymes. The commission has established six main classes, which are further subdivided into sub-classes and sub-sub-classes, according to the nature of the reaction catalyzed and to the type of bond formed or severed. In Table IX several examples of each main class are listed to illustrate the system. 

TABLE 5.3 Some examples of enzyme commission classification and coding... 

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