Chemistry
Enzymes as Biocatalysts
Enzymes are biological catalysts that accelerate chemical reactions in living organisms by lowering the activation energy required for the reaction to occur. They are highly specific, often catalyzing only one type of reaction. Enzymes are essential for various metabolic processes, and their activity can be influenced by factors such as temperature and pH.
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10 Key excerpts on "Enzymes as Biocatalysts"
No longer available |Learn more- Gustavo Blanco, Antonio Blanco(Authors)
- 2017(Publication Date)
- Academic Press(Publisher)
Countless chemical reactions take place at a given time in every living being. Many of them transform exogenous substances, which come with the diet, to obtain energy and the basic materials that will be used for the synthesis of endogenous molecules.Biochemical transformations are performed at a remarkable fast rate and with great efficiency. To reproduce them in the laboratory, these reactions would need extreme changes in temperature, pH, or pressure to take place; these changes are not compatible with cell survival. Under normal physiological conditions (37°C for warm-blooded organisms, pH near neutrality, and constant pressure), most of the reactions would proceed very slowly or may not occur at all. It is the presence of catalysts that allow chemical reactions in living beings to occur with great speed and under the mild conditions that are compatible with life.Enzymes are biological catalysts
A catalyst is an agent capable of accelerating a chemical reaction without being part of the final products or being consumed in the process. In biological media, macromolecules called enzymes act as catalysts.As any catalyst, enzymes work by lowering the reaction activation energy (A e ) (see p. 152). Enzymes are more effective than most inorganic catalysts; moreover, enzymes show a greater specificity of effect. Usually inorganic catalysts function by accelerating a variety of chemical reactions, whereas enzymes catalyze only a specific chemical reaction. Some enzymes act on different substances, but generally, these are compounds with similar structural characteristics and the catalyzed reaction is always of the same type.The substances that are modified by enzymes are called substrates .The specificity of enzymes allows them to have high selectivity to distinguish among different substances and even between optical isomers of a compound. For example, glucokinase, an enzyme that catalyzes d -glucose phosphorylation, does not act on l
eBook - PDF- A Cavaco-Paulo, G Gubitz(Authors)
- 2003(Publication Date)
- Woodhead Publishing(Publisher)
1 Enzymes RICHARD O. JENKINS De Montfort University, UK 1.1 Introduction Enzymes are biological catalysts that mediate virtually all of the biochem-ical reactions that constitute metabolism in living systems. They accelerate the rate of chemical reaction without themselves undergoing any per-manent chemical change, i.e. they are true catalysts. The term ‘enzyme’ was first used by Kühne in 1878, even though Berzelius had published a theory of chemical catalysis some 40 years before this date, and comes from the Greek enzumé meaning ‘in ( en ) yeast ( zumé )’. In 1897, Eduard Büchner reported extraction of functional enzymes from cells. He showed that a cell-free yeast extract could produce ethanol from glucose, a biochemical pathway now known to involve 11 enzyme-catalysed steps. It was not until 1926, however, that the first enzyme (urease from Jack-bean) was purified and crystallised by James Sumner of Cornell University, who was awarded the 1947 Nobel Prize. The prize was shared with John Northrop and Wendell Stanley of the Rockefeller Institute for Medical Research, who had devised a complex precipitation procedure for isolating pepsin. The procedure of Northrop and Stanley has been used to crystallise several enzymes. Subsequent work on purified enzymes, by many researchers, has provided an understanding of the structure and properties of enzymes. All known enzymes are proteins. They therefore consist of one or more polypeptide chains and display properties that are typical of proteins. As considered later in this chapter, the influence of many chemical and physi-cal parameters (such as salt concentration, temperature and pH) on the rate of enzyme catalysis can be explained by their influence on protein struc-ture. Some enzymes require small non-protein molecules, known as cofac-tors, in order to function as catalysts. Enzymes differ from chemical catalysts in several important ways: 1.
eBook - PDF- Edward Bittar(Author)
- 1996(Publication Date)
- Elsevier Science(Publisher)
In turn, the ways that these catalysts function are responsible for many of the most fundamental properties of living organisms. These properties also help explain the action of many medicines and drugs (as well as herbicides, pesticides, poisons, and all types of bioreactive molecules), and the phenomenon of 'biological specificity'. It should be stressed that this chapter takes the minimalist attitude about enzymes themselves. That is, it presents the smallest amount of enzymology needed to understand some basic features of biology and medicine. This presentation will briefly outline some of the mechanisms of enzyme catalysis and will spend most of the time describing the ramifications of these mechanisms for more overt biological properties. Enzyme behavior provides a foundation for understanding the mode of action of many of the chemicals used in medicine.
eBook - PDF- Khushboo Chaudhary, Pankaj Kumar Saraswat(Authors)
- 2023(Publication Date)
- Delve Publishing(Publisher)
ENZYMOLOGY CHAPTER2 12. INTRODUCTION: REVIEW OF A BRIEF HISTORY, ENZYMES AS BIOLOGICAL CATALYSTS, CLASSIFICATION, NOMENCLATURE, PROXIMITY AND ORIENTATION, COVALENT CATALYSIS, ACID-BASE CATALYSIS. Introduction It is the most remarkable and highly specialized protein. Catalyze hundreds of stepwise reactions in biological systems. Regulate many different metabolic activities necessary to sustain life. Living systems use catalysts called enzymes to increase the rate of chemical reactions. The study of enzymes has immense practical importance. In medical science: to know the epidemiology, to diagnose, and to treat diseases (inheritable genetic disorders). • In chemical industries • In food processing • In agriculture • In everyday activities in the home (food preparation, cleaning, beauty care ,etc.) Basic Biology 94 Nomenclature of Enzymology The International Enzyme Commission (EC) has recommended a systematic nomenclature for enzymes. This commission assigns names and numbers to enzymes according to the reaction they catalyze. An example of a systematic enzyme name is EC 3.5.1.5 urea aminohydrolases for the enzyme that catalyzes the hydrolysis of urea. The name of an enzyme frequently provides a clue to its function. In some cases, an enzyme is named by incorporating the suffix -ase into the name of its substrate, e.g., pyruvate decarboxylases catalyzes the removal of a CO 2 group from pyruvate. Certain protein cutting digestive enzymes are an exception to this general rule of enzyme nomenclature, e.g., pepsin, trypsin, chymotrypsin and thrombin. Isozyme:Within an organism, more than one enzyme may catalyze a given reaction. Multiple enzymes catalyzing the same reaction is called isozymes (Scribd, slideshare, molecular-plant-biotechnology, slideplayer, documents, docplayer, bmb.psu, powershow, bioscience, docslide, msluay, scienceprofonlue, biotechuniverse.blogspot).
eBook - PDF- P Karlson(Author)
- 2012(Publication Date)
- Academic Press(Publisher)
C H A P T E R Enzymes and Biocatalysis 1. Chemical Nature of Enzymes The enzymes are a very important group of proteins. All the chemical reactions in the organism (i.e., metabolism) are made possible only through the actions of the catalysts that we call enzymes The substance transformed by an enzyme is termed substrate. Although the German literature still uses both the terms ferment and enzyme, only the latter is used in the English language, and fermentation is restricted to describing bacterial actions. The use of the word enzyme, proposed by Kuhne in 1878, for soluble ferments avoids the historical controversy concerning formed ferments (yeast and other microorganisms, i.e., intact organisms) and unformed ferments (pepsin, trypsin, saccharase). After Buchner's epoch-making discovery that alcoholic fermenta-tion is indeed possible outside the living cell, the concept of formed ferment was dropped, and the designa-tions ferment and enzyme became synonymous. Chemically every enzyme known so far is a protein. About one hundred enzymes have been prepared in pure and crystalline form by the methods of protein chemistry; the first of these was urease (Sumner, 1926). Ribonuclease, trypsin, chymotrypsin, and lysozyme are a few of the enzymes whose structure, i.e., amino acid sequence, have been analyzed completely; the sequences of other enzymes are only partially known. The assumption is that a certain sequence of amino acids at and around the active site of the enzyme is responsible for the catalytic effect. This theory is supported by the observation that part of the molecule may be split off some enzymes without loss of activity. Denaturation abolishes catalytic activity, of course, without changing the sequence of amino acids. Many enzymes are complex proteins; they consist of a protein component and a prosthetic group. Some enzymes in their active form bind the prosthetic group in 74 ν 2. CHEMICAL EQUILIBRIA AND CHEMICAL ENERGETICS 75 a reversible manner.
eBook - PDF- N.A.M. Eskin(Author)
- 2012(Publication Date)
- Academic Press(Publisher)
Second, they show optimal activity in mild conditions. Third, enzymes show a high degree of specificity in the reactions they catalyze, and in the majority of cases one reaction only which makes enzymes easier to work with in food tech-nology. Finally, enzymes are more efficient than chemical catalysts by a factor of around 10 5 -10 8 . Enzymes are most effective in small amounts in a reaction mixture, such that the substrate is greatly in excess of giving maximum velocity for that amount of enzyme. The activity is often expressed as the turnover number (or more often the molecular activity), which is defined as the number of moles of substrate transformed by one mole of enzyme per minute, in standard conditions. For example, one mole of catalase decomposes 36 x 10 6 moles of hydrogen peroxide per second at 30°C and pH 7.O. IV. Commercial Availability of Enzymes 127 IV. Commercial Availability of Enzymes Reference has already been made to the control of undesirable changes in food brought about by enzyme activity. However, in processes such as baking, candy manufacture, and meat tenderization, enzymes can be applied to advan-tage as part of the operation. Industrial enzymes are usually obtained as partially purified concentrates from plant and animal tissues and from micro-organisms. Of all the enzymes which occur in cells, only comparatively few are produced on a commercial scale for use in the food, leather, textiles, and pharmaceutical industries. A. SOURCES OF INDUSTRIAL ENZYMES Microorganisms are rapidly becoming the major source of production of industrial enzymes. Due to the rapid growth rate of microorganisms, the potential for enzyme production is virtually unlimited. A great amount of plant material is required to obtain a reasonable yield of enzyme, whereas the produc-tion of enzymes from animal sources is limited by the supply of material from slaughter houses.
eBook - PDF- P Karlson(Author)
- 1975(Publication Date)
- Academic Press(Publisher)
C H A P T E R Enzymes and Biocatalysis 1. Chemical Nature of Enzymes The enzymes are a very important group of proteins. All the chemical reactions in the organism (i.e., metabolism) are made possible only through the actions of the catalysts that we call enzymes. The substance transformed by an enzyme is termed substrate. Although the German literature still uses both the terms ferment and enzyme, only the latter is used in the English language, and fermentation is restricted to describing bacterial actions. The use of the word enzyme, proposed by Kühne in 1878, for soluble ferments avoids the historical controversy concerning formed ferments (yeast and other microorganisms, i.e., intact organisms) and unformed ferments (pepsin, trypsin, saccharase). After Buchner's epoch-making discovery that alcoholic fermenta-tion is indeed possible outside the living cell, the concept of formed ferment was dropped, and the designa-tions ferment and enzyme became synonymous. Chemically every enzyme known so far is a protein. About one hundred enzymes have been prepared in pure and crystalline form by the methods of protein chemistry ; the first of these was urease (Sumner, 1926). Ribonuclease, trypsin, chymotrypsin, and lysozyme are a few of the enzymes whose structure, i.e., amino acid sequence, have been analyzed completely ; the sequences of other enzymes are only partially known. The assumption is that a certain sequence of amino acids at and around the active site of the enzyme is responsible for the catalytic effect. This theory is supported by the observation that part of the molecule may be split off some enzymes without loss of activity. Denaturation abolishes catalytic activity, of course, without changing the sequence of amino acids. Many enzymes are complex proteins; they consist of a protein component and a prosthetic group. Some enzymes in their active form bind the prosthetic group in 74
eBook - PDFBiochemistry
The Chemical Reactions Of Living Cells
- David Metzler(Author)
- 2012(Publication Date)
- Academic Press(Publisher)
Most of the machinery of cells is made of en-zymes. Hundreds of them have been extracted from living cells, purified and crystallized. Many others are recognized only by their catalytic action and have not yet been isolated in pure form. While most of the known enzymes are soluble globular proteins, the structural proteins of the cell may also exhibit catalysis. Thus, actin and myosin together catalyze the hydrolysis of ATP (Chapter 4, Section F). (However, we do not un-derstand how this enzymatic reaction is coupled to movement of the muscle filaments.) A vast literature documents the properties of enzymes as catalysts and as proteins. Because of this the beginner is apt to lose sight of some simple and fundamental questions: How did we learn that the cell is crammed with enzymes? How do we recognize that a protein is an en-zyme? Part of the answer to both questions is that enzymes are recognized only by their ability to catalyze chemical reactions. Thus, an everyday operation for most biochemists is the measure-ment of catalytic activity of enzymes. Only by measuring rates of catalysis carefully and quanti-tatively has it been possible to isolate and purify these remarkable molecules. The quantitative study of catalysis by enzymes Enzymes: The Protein Catalysts of Cells (enzyme kinetics) is a highly developed mathemat-ical branch of science that is of utmost practical importance to the biochemist. Study of kinetics is our most important means of learning about the mechanisms of catalysis at the active sites of en-zymes. Kinetic studies are used to measure the af-finity and the specificity of binding of substrates and of inhibitors to enzymes, to establish max-imum rates of catalysis by specific enzymes, and in many other ways. The following section contains a brief summary of basic concepts together with some practical tips.
eBook - PDF- Adrie J.J. Straathof, Patrick Adlercreutz(Authors)
- 2000(Publication Date)
- CRC Press(Publisher)
8. BIOCATALYST PERFORMANCE ANTONIO BALLESTEROS1 AND LASZLO BOROSS2 1 Departamento de Biocatalisis, Institute de Catalisis, CSIC, 28049 Madrid, Spain Email: [email protected] 2 Department of Chemistry and Biochemistry, University for Horticulture and Food Industry, Budapest, Hungary Email: [email protected] ABSTRACT In the case of most enzymic transformations the reaction rate can be described as a hyperbolic function of the concentration of substrate; the characteristic parameters of these hyperboles are the Vmax and the K*i values, which can be determined easily by different linearized plots. Different factors such as temperature, pH, chemical modification of the functional groups in the side chains of the protein, reversible inhibitors, activators, allosteric effectors, influence the catalytic activity of the enzymes. Since the protein scaffold is commonly not very stable, many methods have been used for stabilization: presence of additives, immobilization by multiple-point attachment, stabilization by chemical or biochemical modification and by protein engineering, and several others. 8.1 ENZYME KINETICS AND MECHANISMS 8.1.1 Introduction For application of a biocatalyst we must know its basic properties, the substrate specificity and the kinetic characteristics. The substrate specificity is a relatively uncomplicated topic, it can be determined with simple experiments, and for the most important enzymes many data are available. Determination of the kinetic properties of an enzyme is a more complex problem. A detailed description of an enzymic catalysis requires extensive data about the structure of the whole protein molecule, the structure of its active centre, the mechanism of the reaction, the rate constants of the individual steps of the catalytic process, the stability of the active conformation, the action of stabilizers, activators, inhibitors etc.
eBook - PDF- Gerald Karp, Janet Iwasa, Wallace Marshall(Authors)
- 2021(Publication Date)
- Wiley(Publisher)
The pro- ton is subsequently donated to the serine residue of the enzyme. 3.2 Enzymes as Biological Catalysts 115 retain a high level of enzymatic activity. It should be possible, therefore, to use X-ray diffraction techniques to study reaction mechanisms. There is one major limitation, namely, time. In a standard crystallographic study, enzyme crystals must be sub- jected to an X-ray beam for a period of hours or days while the necessary data are collected. The portrait that emerges from such studies captures the structure of the molecule averaged out over time. Recent innovations, however, have made it possi- ble to use X-ray crystallographic techniques to observe the fleet- ing structural changes that take place in the active site while an enzyme is catalyzing a single reaction cycle. This approach, which is called time-resolved crystallography, can include: • Use of ultra-high-intensity X-ray beams generated by a synchrotron, an instrument used by nuclear physicists to study subatomic particles. This can cut the X-ray exposure period to a matter of picoseconds, which is the same time scale required for an enzyme to catalyze a single chemical transformation. • Cooling the enzyme crystals to temperatures within 20 to 40 degrees of absolute zero, which slows the reaction by a factor as high as 10 billion, greatly increasing the lifetime of transient intermediates. • Use of techniques to simultaneously trigger a reaction throughout an entire crystal so that all of the enzyme mol- ecules in the crystal are in the same stage of the reaction at the same time. For example, in a reaction in which ATP is a substrate, the enzyme crystals can be infiltrated with ATP molecules that have been made nonreactive by link- ing them to an inert group (e.g., a nitrophenyl group) by a photosensitive bond.
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