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23 - Enzymes and Receptors
- Edited by Andreas Hofmann, Griffith University, Queensland, Samuel Clokie
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- Book:
- Wilson and Walker's Principles and Techniques of Biochemistry and Molecular Biology
- Published online:
- 06 August 2018
- Print publication:
- 19 April 2018, pp 809-863
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23 - Enzymes and Receptors
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- By Megan Cross, Griffith University, Andreas Hofmann, Griffith University, Queensland
- Edited by Andreas Hofmann, Griffith University, Queensland, Samuel Clokie
-
- Book:
- Wilson and Walker's Principles and Techniques of Biochemistry and Molecular Biology
- Published online:
- 06 August 2018
- Print publication:
- 19 April 2018, pp 809-863
-
- Chapter
- Export citation
-
Summary
DEFINITION AND CLASSIFICATION OF ENZYMES
Catalytic reactions in biological processes are facilitated by two types of catalysts, enzymes and ribozymes. Whereas enzymes are proteins, ribozymes consist of ribonucleic acid (RNA). Most enzymes are much larger than the substrates they process, but this is not a requirement (for example, restriction enzymes that cleave DNA). The catalytic features of enzymes arise through a particular three-dimensional arrangement of functional groups in a small number of amino acids (see Section 23.4.2) in the active site of the enzyme. The geometrical arrangement of such groups enables productive interactions with the bound substrate and leads to formation of a transition state for which the energy barrier (activation energy) is significantly reduced as compared to the non-catalysed reaction (see Figure 23.1). Consequently, the reaction rate is increased by several orders of magnitude relative to the non-catalysed reaction. Importantly, enzymes do not alter the position of equilibrium of the reversible reactions they catalyse, rather they accelerate establishment of the position of equilibrium for the reaction.
Many enzymes are the key players in metabolic or signalling pathways. In these coordinated pathways, enzymes are collectively responsible for maintaining the metabolic needs of cells under varying physiological conditions (Section 23.5). Through their individual catalytic activities, they control the rate of a particular metabolic or signalling pathway. A range of regulatory mechanisms operates to allow short-, medium- and long-term changes in activity (Section 23.5.1). Therefore, the over- or under-expression of an enzyme can lead to cell dysfunction, which may manifest itself as a particular disease. Hence, enzymes have been the most important target in the development of therapeutics, and typical drugs for the treatment of pathological conditions act as inhibitors of particular enzymes (Sections 23.5.3). Other clinically relevant applications include monitoring of enzyme levels in assessment of disease states. For example, damage to the heart muscle as a result of oxygen deprivation following a heart attack results in the release of cellular enzymes into extra-cellular fluids and eventually into the blood. Such release can be monitored to aid diagnosis of the organ damage and to make a prognosis for the patient's future recovery (Section 10.3).
Contributors
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- By Tod C. Aeby, Melanie D. Altizer, Ronan A. Bakker, Meghann E. Batten, Anita K. Blanchard, Brian Bond, Megan A. Brady, Saweda A. Bright, Ellen L. Brock, Amy Brown, Ashley Carroll, Jori S. Carter, Frances Casey, Weldon Chafe, David Chelmow, Jessica M. Ciaburri, Stephen A. Cohen, Adrianne M. Colton, PonJola Coney, Jennifer A. Cross, Julie Zemaitis DeCesare, Layson L. Denney, Megan L. Evans, Nicole S. Fanning, Tanaz R. Ferzandi, Katie P. Friday, Nancy D. Gaba, Rajiv B. Gala, Andrew Galffy, Adrienne L. Gentry, Edward J. Gill, Philippe Girerd, Meredith Gray, Amy Hempel, Audra Jolyn Hill, Chris J. Hong, Kathryn A. Houston, Patricia S. Huguelet, Warner K. Huh, Jordan Hylton, Christine R. Isaacs, Alison F. Jacoby, Isaiah M. Johnson, Nicole W. Karjane, Emily E. Landers, Susan M. Lanni, Eduardo Lara-Torre, Lee A. Learman, Nikola Alexander Letham, Rachel K. Love, Richard Scott Lucidi, Elisabeth McGaw, Kimberly Woods McMorrow, Christopher A. Manipula, Kirk J. Matthews, Michelle Meglin, Megan Metcalf, Sarah H. Milton, Gaby Moawad, Christopher Morosky, Lindsay H. Morrell, Elizabeth L. Munter, Erin L. Murata, Amanda B. Murchison, Nguyet A. Nguyen, Nan G. O’Connell, Tony Ogburn, K. Nathan Parthasarathy, Thomas C. Peng, Ashley Peterson, Sarah Peterson, John G. Pierce, Amber Price, Heidi J. Purcell, Ronald M. Ramus, Nicole Calloway Rankins, Fidelma B. Rigby, Amanda H. Ritter, Barbara L. Robinson, Danielle Roncari, Lisa Rubinsak, Jennifer Salcedo, Mary T. Sale, Peter F. Schnatz, John W. Seeds, Kathryn Shaia, Karen Shelton, Megan M. Shine, Haller J. Smith, Roger P. Smith, Nancy A. Sokkary, Reni A. Soon, Aparna Sridhar, Lilja Stefansson, Laurie S. Swaim, Chemen M. Tate, Hong-Thao Thieu, Meredith S. Thomas, L. Chesney Thompson, Tiffany Tonismae, Angela M. Tran, Breanna Walker, Alan G. Waxman, C. Nathan Webb, Valerie L. Williams, Sarah B. Wilson, Elizabeth M. Yoselevsky, Amy E. Young
- Edited by David Chelmow, Virginia Commonwealth University, Christine R. Isaacs, Virginia Commonwealth University, Ashley Carroll, Virginia Commonwealth University
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- Book:
- Acute Care and Emergency Gynecology
- Published online:
- 05 November 2014
- Print publication:
- 30 October 2014, pp ix-xiv
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