Enzyme Kinetics and Inhibition Quiz

Enzyme Kinetics and Inhibition

• Enzyme classifications include oxidoreductases, transferases, hydrolases, lyases, isomerases, and ligases.
• Enzymes lower activation energy (Ea) to increase reaction rate without changing thermodynamic parameters.
• The Michaelis-Menten equation relates substrate concentration to Vmax and KM, with Vmax representing maximal velocity and KM the Michaelis constant.
• Saturation kinetic curve shows enzyme saturation with substrate and the impact of high or low KM values.
• Lineweaver-Burke plot provides a double reciprocal of the Michaelis-Menten equation, offering an easier method for interpreting graphical data.
• Turnover number (kcat) measures the number of reactions an enzyme can catalyze per unit of time, indicating catalytic efficiency.
• Diffusion controlled limit occurs when the rate-limiting step becomes the diffusion of enzyme and substrate, with a rate between 108 and 109 M−1 sec−1.
• Inhibitors can be irreversible or reversible, preventing the generation of products.
• Suicide inhibitors irreversibly block enzyme function by covalently modifying the active site, examples include pesticides and nerve agents.
• Competitive inhibition involves molecules similar to the substrate shape, competing directly with the substrate and can be overcome with high substrate concentration.
• Uncompetitive inhibition binds to the ES complex, decreasing both Vmax and KM.
• Mixed inhibition combines features of competitive and uncompetitive inhibitors, being effective regardless of substrate concentration.

Enzyme Catalysis and Regulation

• Carbonic anhydrase is found in erythrocytes and catalyzes the conversion of carbon dioxide to carbonic acid using Zn2+ in the active site.
• Proteases are enzymes that degrade proteins and include trypsin, chymotrypsin, and elastase, and are important in protein maturation, blood clotting, and protein trafficking.
• Different classes of proteases, including serine, aspartyl, metallo-, and cysteine proteases, employ similar chemistry with conserved topology and overall structure.
• Chymotrypsin is a serine protease that cleaves dietary protein and contains a catalytic triad with Aspartate, Histidine, and Serine.
• Affinity labeling is a technique to specifically label active site residues with examples like Diisopropylfluorophosphate and Tosyl-L-phenylalanine chloromethyl ketone.
• Enzyme regulation can be achieved through altering gene expression, sequestration in compartments, limiting substrate access, and covalent modification and allosteric regulation methods.
• Covalent modification involves the covalent addition or removal of groups from proteins, with proteolytic cleavage and phosphorylation as common means of activation.
• Zymogens are inactive enzyme precursors that require proteolytic activation, with chymotrypsinogen being the inactive form of chymotrypsin.
• Phosphorylation is another example of protein activation facilitated by protein kinases adding phosphate groups and phosphatases removing them, regulated through signaling cascades.
• Src is an example of regulation via phosphorylation.
• Allosteric regulation can increase or decrease enzymatic activity by binding at a site other than the active site, with relaxed (R) and tense (T) states and sigmoidal activity curves.
• Copyright © 2019 John Wiley & Sons, Inc. All rights reserved. Reproduction or translation of this work beyond that permitted in Section 117 of the 1976 United States Act without the express written permission of the copyright owner is unlawful. Request for further information should be addressed to the Permissions Department, John Wiley & Sons, Inc. The purchaser may make back-up copies for his/her own use only and not for distribution or resale. The Publisher assumes no responsibility for errors, omissions, or damages, caused by the use of these programs or from the use of the information contained herein. Copyright © 2019 John Wiley & Sons, Inc.