At any moment, thousands of chemical reactions are taking place in any living cell. Enzymes are essential for these reactions to proceed at rates fast enough to sustain life. What are enzymes, and what do they do? | Chapter 15 Enzyme Specificity and Regulation to accompany Biochemistry, 2/e by Reginald Garrett and Charles Grisham All rights reserved. Requests for permission to make copies of any part of the work should be mailed to: Permissions Department, Harcourt Brace & Company, 6277 Sea Harbor Drive, Orlando, Florida 32887-6777 Outline Specificity from Molecular Recognition Controls over Enzymatic Activity Allosteric Regulation of Enzyme Activity Allosteric Model Glycogen Phosphorylase SPECIAL FOCUS: Hemoglobin and Myoglobin Specificity The Result of Molecular Recognition Substrate (small) binds to enzyme (large) via weak forces - what are they? H-bonds, van der Waals, ionic sometimes hydrophobic interactions Understand the lock-and-key and induced-fit models Relate induced-fit to transition states Controls over Enzyme Activity Six points: Rate slows as product accumulates Rate depends on substrate availability Genetic controls - induction and repression Enzymes can be modified covalently Allosteric effectors may be important Zymogens, isozymes and modulator proteins may play a role Allosteric Regulation Action at "another site" Enzymes situated at key steps in metabolic pathways are modulated by allosteric effectors These effectors are usually produced elsewhere in the pathway Effectors may be feed-forward activators or feedback inhibitors Kinetics are sigmoid ("S-shaped") Models for Allosteric Behavior Monod, Wyman, Changeux (MWC) Model: allosteric proteins can exist in two states: R (relaxed) and T (taut) In this model, all the subunits of an oligomer must be in the same state T state predominates in the absence of substrate S S binds much tighter to R than to T More about MWC Cooperativity is achieved because S binding increases the population of R, which increases the sites available to S Ligands such as S are positive homotropic effectors Molecules that influence the binding of something other than themselves are heterotropic . | Chapter 15 Enzyme Specificity and Regulation to accompany Biochemistry, 2/e by Reginald Garrett and Charles Grisham All rights reserved. Requests for permission to make copies of any part of the work should be mailed to: Permissions Department, Harcourt Brace & Company, 6277 Sea Harbor Drive, Orlando, Florida 32887-6777 Outline Specificity from Molecular Recognition Controls over Enzymatic Activity Allosteric Regulation of Enzyme Activity Allosteric Model Glycogen Phosphorylase SPECIAL FOCUS: Hemoglobin and Myoglobin Specificity The Result of Molecular Recognition Substrate (small) binds to enzyme (large) via weak forces - what are they? H-bonds, van der Waals, ionic sometimes hydrophobic interactions Understand the lock-and-key and induced-fit models Relate induced-fit to transition states Controls over Enzyme Activity Six points: Rate slows as product accumulates Rate depends on substrate availability Genetic controls - induction and repression .
