Structure and Functions (Magill’s Medical Guide, Sixth Edition)
Enzymes are remarkable molecules because they increase rates of biochemical reactions. Each enzyme within a cell selectively speeds up, or catalyzes, one particular reaction or type of reaction. The vast majority of enzymes belong to the class of large molecules known as proteins. Proteins are built by combining amino acids. There are twenty amino acids, which can be divided into three classes: hydrophobic, charged, and polar. Hydrophobic amino acids behave chemically like oils, avoiding contact with water. Charged amino acids are ionic, containing one extra or one less electron than do neutral molecules. Polar amino acids are attracted to water and other polar amino acids. Each of these three classes of amino acids has a distinct chemistry. The specific order of the amino acid sequence defines the structure and function of every protein. Inside cells, enzymes catalyze reactions so that they occur millions of times faster than they would without the presence of these proteins. Each cell in the body produces many different enzymes. Different sets of enzymes are found in different tissues, reflecting the specialized function of each particular enzyme. Thousands of different enzymes are at work in the body; many have yet to be discovered.
Protein enzymes work by bringing the reactants in a chemical reaction together in the most favorable geometrical arrangement, so that bonds can be easily broken and reformed. This is...
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Disorders and Diseases (Magill’s Medical Guide, Sixth Edition)
Defects in enzymes, known as mutations, can cause disease. A protein molecule is mutated when one or more of the original amino acids in the protein is replaced by a different amino acid. For example, if an enzyme consists of one hundred amino acids, and amino acid number 35 is changed from one kind of amino acid to a different kind, the protein is now a mutant. A mutated enzyme has a slightly altered shape compared to the original enzyme. If the change in shape causes the enzyme to perform its chemistry more slowly than the original enzyme, then the cell and tissue have an impaired function. In particular, if an amino acid is changed from one of the three classes (hydrophobic, charged, or polar) to a different class, then the mutation is more likely to cause a change in the structure and function of the enzyme. Not all mutations are harmful, but a single mutation in a key region of an enzyme can be fatal to a living organism.
Many diseases are diagnosed by measuring enzyme concentrations and activities in the body. Enzyme concentration refers to the amount of enzyme present, while enzyme activity refers to the ability of the enzyme to perform its chemistry. Enzyme concentrations and activities can be measured in blood or in tissue. Disease of tissues and organs can cause cellular damage, so that enzymes that are normally not present in significant quantities in blood are raised to very high levels as they flow from...
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Perspective and Prospects (Magill’s Medical Guide, Sixth Edition)
Enzymatic reactions have been used by humankind since prehistoric times. It has been known for more than six thousand years that fermentation processes transform grapes into wine, but it was not until the nineteenth century that it was understood that the conversion of grape sugar to alcohol is a process catalyzed by enzymes found in yeast. In the eighteenth century, Antoine Lavoisier showed that a solution of sugar could be fermented if provided with the sediment of a previous fermentation and that the sugar was converted to alcohol and carbon dioxide in this process. At this time, it was thought that there was a vital force responsible for the workings of a living cell. This notion of a vital force slowed the development of the discipline of biochemistry considerably, as many good scientists struggled to understand the fermentation process. In 1828, Friedrich Wöhler synthesized urea in a test tube, providing strong evidence against the concept of a vital force. In 1833, Anselme Payen and Jean Persoz discovered the first enzyme, diastase (now known as amylase), which converted starch into sugar. The next year, Johann Eberle showed that the presence of a stomach is not required for gastric digestion to take place. In 1836, Theodor Schwann made the very important discovery that the active ingredient in digestion, which he called pepsin, could be extracted from the stomach wall.
The next year, Jöns Jakob Berzelius...
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For Further Information: (Magill’s Medical Guide, Sixth Edition)
Campbell, Neil A., et al. Biology: Concepts and Connections. 6th ed. San Francisco: Pearson/Benjamin Cummings, 2008. This classic introductory textbook provides an excellent discussion of essential biological structures and mechanisms. Its extensive and detailed illustrations help to make even difficult concepts accessible to the nonspecialist. Of particular interest is the chapter on enzymes, titled “An Introduction to Metabolism.”
Copeland, Robert A. Enzymes: A Practical Introduction to Structure, Mechanism, and Data Analysis. 2d ed. New York: Wiley, 2000. An introductory text that examines the structural complexities of proteins and enzymes and the mechanisms by which enzymes perform their catalytic functions.
Fruton, Joseph S. Molecules and Life. New York: Wiley-Interscience, 1972. Fruton, a Yale biochemist, has filled his book with historical essays on the interplay of chemistry and biology. The first part of the book, “From Ferments to Enzymes,” is an interesting account of how science progressed from the known results of fermentation to the chemical knowledge that enzymes were the molecules responsible for this and all other biochemical processes.
Kornberg, Arthur. For the Love of Enzymes: The Odyssey of a Biochemist. Cambridge, Mass.: Harvard University Press, 1989. Both an autobiography of a great biochemist and a history of the study of enzymes....
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Enzyme (Encyclopedia of Science)
An enzyme is a biological catalyst. A catalyst is a chemical compound that speeds up the rate of some chemical reaction. When that chemical reaction occurs in a living organism, the catalyst is known as an enzyme.
Catalyzed and uncatalyzed reactions
Figure 1 shows how an enzyme (or any other catalyst) affects the rate of a chemical reaction. Consider the reaction in which a complex carbohydrate, such as starch, is broken down in the body to produce the simpler sugars known as sucrose. We can express this reaction by the following chemical equation:
The compound present at the beginning of the reaction (starch) is known as the reactant. The compound that is formed as a result of the reaction (sucrose) is known as the product.
In most instances, energy has to be supplied to the reactant or reactants in order for a reaction to occur. For example, if you heat a suspension of starch in water, the starch begins to break down to form sucrose.
The line labeled "Uncatalyzed reaction" in Figure 1 represents changes in energy that take place in the reaction without a catalyst. Notice that the amount of energy needed to make the reaction happen increases from its beginning point to a maximum point, and then drops to a minimum point. The graph shows that an amount of...
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Enzymes (Science Experiments)
What's in a name?
Tough and Tender: Does papain speed up the aging process?
You could not run a race or digest food without enzymesAny of numerous complex proteins produced by living cells that act as catalysts.. Actually, you could not grow up without enzymes working in your body. Present in all living things, enzymes are , that is, little chemical spark plugs that activate some 1,000 to 2,000 reactionsResponse to an action prompted by stimulus. in each cell. Enzymes control the way our bodies work. They help other life forms function as well. For example, the silkworm cannot break out of its cocoon without enzymes.
Rene Antoine de Reaumur was a French scientist who wanted to know how food was digested. In 1750, he tried a unique experiment. Tying a very tiny metal cage containing a small piece of meat on a long string, he taught his pet hawk to swallow the cage. The string hung out of the bird's mouth, and de Reaumur very carefully pulled out the cage after...
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Enzymes (World of Microbiology and Immunology)
Enzymes are molecules that act as critical catalysts in biological systems. Catalysts are substances that increase the rate of chemical reactions without being consumed in the reaction. Without enzymes, many reactions would require higher levels of energy and higher temperatures than exist in biological systems. Enzymes are proteins that possess specific binding sites for other molecules (substrates). A series of weak binding interactions allow enzymes to accelerate reaction rates. Enzyme kinetics is the study of enzymatic reactions and mechanisms. Enzyme inhibitor studies have allowed researchers to develop therapies for the treatment of diseases, including AIDS.
French chemist Louis Pasteur (1822895) was an early investigator of enzyme action. Pasteur hypothesized that the conversion of sugar into alcohol by yeast was catalyzed by "ferments," which he thought could not be separated from living cells. In 1897, German biochemist Eduard Buchner (1860917) isolated the enzymes that catalyze the fermentation of alcohol from living yeast cells. In 1909, English physician Sir Archibald Garrod (1857936) first characterized enzymes genetically through the one gene-one enzyme hypothesis. Garrod studied the human disease alkaptonuria, a hereditary disease characterized by the darkening of excreted urine after exposure to air. He hypothesized that alkaptonurics lack an enzyme that breaks down alkaptans to normal excretion products, that alkaptonurics inherit this inability to produce a specific enzyme, and that they inherit a mutant form of a gene from each of their parents and have two mutant forms of the same gene. Thus, he hypothesized, some genes contain information to specify particular enzymes.
The early twentieth century saw dramatic advancement in enzyme studies. German chemist Emil Fischer (1852919) recognized the importance of substrate shape for binding by enzymes. German-American biochemist Leonor Michaelis (1875949) and Canadian biologist Maud Menten (1879960) introduced a mathematical approach for quantifying enzyme-catalyzed reactions. American chemists James Sumner (1887955) and John Northrop (1891987) were among the first to produce highly ordered enzyme crystals and firmly establish the proteinaceous nature of these biological catalysts. In 1937, German-born British biochemist Hans Krebs (1900981) postulated how a series of enzymatic reactions were coordinated in the citric acid cycle for the production of ATP from glucose metabolites. Today, enzymology is a central part of biochemical study, and the fields of industrial microbiology and genetics employ enzymes in numerous ways, from food production to gene cloning, to advanced therapeutic techniques.
Enzymes are proteins that encompass a large range of molecular size and mass. They may be composed of more than one polypeptide chain. Each polypeptide chain is called a subunit and may have a separate catalytic function. Some enzymes require non-protein groups for enzymatic activity. These components include metal ions and organic molecules called coenzymes. Coenzymes that are tightly or covalently attached to enzymes are termed prosthetic groups. Prosthetic groups contain critical chemical groups which allow the overall catalytic event to occur.
Enzymes bind their substrates at special folds and clefts in their structures called active sites. Because active sites have chemical groups precisely located and orientated for binding the substrate, they generally display a high degree of substrate specificity. The active site of an enzyme consists of two key regions, the catalytic site, which interacts with the substrate during the reaction, and the binding site, the chemical groups of the enzyme that bind the substrate, allowing the interactions at the catalytic site to occur. The crevice of the active site creates a microenvironment whose properties are critical for catalysis. Environmental factors influencing enzyme activity include pH, polarity and hydrophobicity of amino acids in the active site, and a precise arrangement of the chemical groups of the enzyme and its substrate.
Enzymes have high catalytic power, high substrate specificity, and are generally most active in aqueous solvents at mild temperature and physiological pH. Most enzymes catalyze the transfer of electrons, atoms, or groups of atoms. There are thousands of known enzymes, but most can be categorized according to their biological activities into six major classes: oxidoreductases, transferases, hydrolases, lyases, isomerases, and ligases.
Enzymes generally have an optimum pH range in which they are most active. The pH of the environment will affect the ionization state of catalytic groups at the active site and the ionization of the substrate. Electrostatic interactions are therefore controlled by pH. The pH of a reaction may also control the conformation of the enzyme by influencing amino acids critical for the three-dimensional shape of the macromolecule.
Inhibitors can diminish the activity of an enzyme by altering the binding of substrates. Inhibitors may resemble the structure of the substrate, thereby binding the enzyme and competing for the correct substrate. Inhibitors may be large organic molecules, small molecules, or ions. They can be used for chemotherapeutic treatment of diseases.
Regulatory enzymes are characterized by increased or decreased activity in response to chemical signals. Metabolic pathways are regulated by controlling the activity of one or more enzymatic steps along that path. Regulatory control allows cells to meet changing demands for energy and metabolites.
See also Biochemical analysis techniques; Biotechnology; Bioremediation; Cloning, application of cloning to biological problems; Enzyme induction and repression; Enzyme-linked immunosorbant assay (ELISA); Food preservation; Food safety; Immunologic therapies; Immunological analysis techniques