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Chapter 20 Enzymes and Vitamins 20.5 Control of Enzyme Activity Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings 1 Zymogens Zymogens (proenzymes) Are inactive forms of enzymes. Are activated when one or more peptides are removed. Such as proinsulin is converted to insulin by removing a small Copyright © 2007 by Pearson Education, Inc. peptide chain. Publishing as Benjamin Cummings 2 Digestive Enzymes Digestive enzymes are Produced as zymogens in one organ and transported to another such as the pancreas when needed. Activated by removing small peptide sections. TABLE 20.7 Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings 3 Digestive Enzymes Zymogen (from pancreas) Active Enzyme (in small intestine) enteropeptidase trypsinogen trypsin + peptide trypsin chymotrypsinogen chymotrypsin + 2 dipeptides trypsin procarboxypeptidase carboxypeptidase + peptide 4 Allosteric Enzymes An allosteric enzyme is An enzyme in a reaction sequence that binds a regulator substance. A positive regulator when it enhances the binding of substrate and accelerates the rate of reaction. A negative regulator when it prevents the binding of the substrate to the active site and slows down the rate of reaction. 5 Feedback Control In feedback control A product acts as a negative regulator. An end product binds with the first enzyme (E1) in a sequence when sufficient product is present. Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings 6 Learning Check Identify each statement as: zymogen (Z) allosteric enzyme (A) positive regulator (PR) feedback control (FC) 1. An enzyme in a pathway that controls the rate of the reaction. 2. Speeds up a reaction by combining with an enzyme in the pathway. 3. Removal of a peptide activates the enzyme. 4. Some product binds to the first enzyme to limit the synthesis of product. 7 Solution Identify each statement as: zymogen (Z) allosteric enzyme (A) positive regulator (PR) feedback control (FC) 1. A An enzyme in a pathway that controls the rate of the reaction. 2. PR Speeds up a reaction by combining with an enzyme in the pathway. 3. Z Removal of a peptide activates the enzyme. 4. FC Some product binds to the first enzyme to limit the synthesis of product. 8