![]() glucose oxidase, alcohol dehydrogenase, pyruvate decarboxylase). Often the trivial name also indicates the substrate on which the enzyme acts (e.g. oxidase, dehydrogenase, carboxylase), although individual proteolytic enzymes generally have the suffix ‘-in’ (e.g. Table 6.1 Turnover Rate of Some Common Enzymes Showing Wide VariationĮnzymes typically have common names (often called ‘trivial names’) which refer to the reaction that they catalyze, with the suffix ‘-ase’ (e.g. As we shall see later, this specificity is of paramount importance in many analytical assays and devices (biosensors) that measure a specific substrate (e.g. For example, glucose oxidase shows almost total specificity for its substrate, β-D-glucose, and virtually no activity with any other monosaccharides. Other enzymes demonstrate much higher specificity, which is described as absolute specificity. For example, alkaline phosphatase (an enzyme that is commonly encountered in first-year laboratory sessions on enzyme kinetics) can remove a phosphate group from a variety of substrates. Some enzymes demonstrate group specificity. For example, a single molecule of carbonic anhydrase can catalyse the conversion of over half a million molecules of its substrates, carbon dioxide (CO 2) and water (H 2O), into the product, bicarbonate (HCO 3 −), every second-a truly remarkable achievement.Īs well as being highly potent catalysts, enzymes also possess remarkable specificity in that they generally catalyze the conversion of only one type (or at most a range of similar types) of substrate molecule into product molecules. Examples of turnover rate values are listed in Table 6.1. This constant represents the number of substrate molecules that can be converted to product by a single enzyme molecule per unit time (usually per minute or per second). The enormous catalytic activity of enzymes can perhaps best be expressed by a constant, k cat, that is variously referred to as the turnover rate, turnover frequency or turnover number. We usually describe enzymes as being capable of catalyzing the conversion of substrate molecules into product molecules as follows: Notwithstanding these notable exceptions, much of classical enzymology, and the remainder of this essay, is focused on the proteins that possess catalytic activity.Īs catalysts, enzymes are only required in very low concentrations, and they speed up reactions without themselves being consumed during the reaction. These so-called ‘abzymes’ have significant potential both as novel industrial catalysts and in therapeutics. In the same decade, biochemists also developed the technology to generate antibodies that possess catalytic properties. These RNAs, which are called ribozymes, play an important role in gene expression. For the next 60 years or so it was believed that all enzymes were proteins, but in the 1980s it was found that some ribonucleic acid (RNA) molecules are also able to exert catalytic effects. ![]() ![]() In the late nineteenth century and early twentieth century, significant advances were made in the extraction, characterization and commercial exploitation of many enzymes, but it was not until the 1920s that enzymes were crystallized, revealing that catalytic activity is associated with protein molecules. The word ‘enzyme’ was first used by the German physiologist Wilhelm Kühne in 1878, when he was describing the ability of yeast to produce alcohol from sugars, and it is derived from the Greek words en (meaning ‘within’) and zume (meaning ‘yeast’). For example, they have important roles in the production of sweetening agents and the modification of antibiotics, they are used in washing powders and various cleaning products, and they play a key role in analytical devices and assays that have clinical, forensic and environmental applications. They can also be extracted from cells and then used to catalyse a wide range of commercially important processes. ![]() Chapter 6: Enzyme Principles and Biotechnological Applications 6.1 The Nature and Classification of Enzymes 6.2 Enzyme Names and Classification 6.3 Enzyme Structure and Substrate Binding 6.4 Enzymes and Reaction Equilibrium 6.5 Properties and Mechanisms of Enzyme Action 6.6 Enzymes are Affected by pH and Temperature 6.7 Enzymes are Sensitive to InhibitorsĦ.8 Allosteric Regulators and the Control of Enzyme Activity 6.9 Origin, Purification, and Uses of EnzymesĦ.1 The Nature and Classification of EnzymesĮnzymes are biological catalysts (also known as biocatalysts) that speed up biochemical reactions in living organisms.
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