General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.1 Chapter 20 Enzymes and Vitamins 20.2 Enzyme Action

General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.2 Active Site The active site  is a region within an enzyme that fits the shape of the reacting molecule, called a substrate  contains amino acid R groups that bind the substrate  releases products when the reaction is complete

General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.3 Enzyme-Catalyzed Reaction  The proper fit of a substrate (S) in an active site on an enzyme (E) forms an enzyme–substrate (ES) complex. E + S ES  Within the ES complex, the reaction occurs to convert substrate to product (P). ES E + P  The products, which are no longer attracted to the active site, are released.  Overall, substrate is converted to product. E + S ES E + P

General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.4 Enzyme-Catalyzed Reaction (continued) In an enzyme-catalyzed reaction,  a substrate attaches to the active site  an enzyme–substrate (ES) complex forms  reaction occurs and products are released  an enzyme (E) is used over and over E + S ES E + P

General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.5 Enzymes may recognize and catalyze  a single substrate  a group of similar substrates  a particular type of bond Enzyme Specificity

General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.6 Lock-and-Key Model In the lock-and-key model of enzyme action,  the active site has a rigid shape  only substrates with the matching shape can fit  the substrate is the key that fits that lock

General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.7 Induced-Fit Model In the induced-fit model of enzyme action,  enzyme structure is flexible, not rigid  shapes of enzyme and substrate adjust for best fit at the active site to improve catalysis of reaction  substrate specificity increases

General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.8 Example of an Enzyme-Catalyzed Reaction

General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.9 Learning Check A. The active site is 1) the entire enzyme 2) a section of the enzyme 3) the substrate B. In the induced-fit model, the shape of the enzyme when substrate binds 1) stays the same 2) adapts to the shape of the substrate

General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.10 Solution A. The active site is 2) a section of the enzyme B. In the induced-fit model, the shape of the enzyme when substrate binds 2) adapts to the shape of the substrate

General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.11 Isoenzymes  catalyze the same reaction in different tissues in the body  such as lactate dehydrogenase (LDH), which converts lactate to pyruvate, consist of five isoenzymes  can be used to identify the organ or tissue involved in damage or disease  such as LDH have one form more prevalent in heart muscle and another form in skeletal muscle and liver tissue

General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.12 Isoenzymes (continued)

General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.13 Diagnostic Enzymes Diagnostic enzymes  determine the amount of damage in tissues  that are elevated may indicate damage or disease in a particular organ

General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.14 Diagnostic Enzymes (continued) Levels of the enzyme creatine kinase (CK), lactic dehydrogenase (LDH), and aspartate transaminase (AST)  are elevated following a heart attack  are used to determine the severity of the attack