Enzymes
Page 1: Overview of Enzymatic Components
Key Terms
Substrate: The reactant upon which an enzyme works.
Enzyme: A protein that catalyzes chemical reactions by lowering activation energy.
Active Site: The specific region of the enzyme where the substrate binds.
Reaction Products: The end result after the substrate has been converted by the enzyme.
Types of Enzymes:
Amylase: Enzyme that catalyzes the hydrolysis of carbohydrates.
Protease: Enzyme that breaks down proteins.
Lipase: Enzyme specialized in fat breakdown.
Page 2: Learning Goals
Objectives
Classification of enzymes by reaction type and specificity.
Correlation between enzyme names and functions.
Impact of enzymes on activation energy.
Importance of active site and enzyme specificity.
Difference between lock-and-key and induced fit models.
Roles of cofactors and coenzymes.
Effects of pH and temperature on enzyme reaction rates.
Mechanisms of enzyme activity regulation.
Chemical inhibition of enzyme activity.
Page 3: Enzyme Classification
Classification Categories
Oxidoreductase: Catalyzes oxidation-reduction reactions.
Transferase: Transfers functional groups from one molecule to another.
Hydrolase: Catalyzes reactions involving the addition of water to break bonds.
Lyase: Catalyzes the removal or addition of groups to form or break double bonds.
Isomerase: Catalyzes rearrangements of molecules.
Ligase: Catalyzes the joining of two substrates, breaking or forming C-C, C-S, C-O, or C-N bonds.
Page 4: Oxidoreductases
Functionality
Oxidoreductases: Enzymes that facilitate redox reactions.
Examples include lactate dehydrogenase, which converts lactate to pyruvate.
Page 5: Transferases
Breakdown
Transferases: Enzymes that transfer functional groups.
Transaminases: Transfer amino groups.
Transmethylases: Transfer methyl groups.
Kinases: Transfer phosphate groups.
Page 6: Hydrolases
Functionality
Hydrolases: Enzymes that cleave bonds through water addition.
Examples include phosphatases, peptidases, lipases, and glycosidases (e.g., amylase).
Page 7: Lyases
Mechanism
Lyases: Catalyze addition or removal of groups to form or break double bonds.
Examples include decarboxylases and synthases.
Page 8: Isomerases
Types of Isomerases
Isomerases: Facilitate intramolecular rearrangements.
Examples include epimerases and mutases, such as phosphoglycerate mutase.
Page 9: Ligases
Overview
Ligases: Enzymes that make or break C-C, C-S, C-O, or C-N bonds.
Page 10: Nomenclature of Enzymes
Naming Conventions
Enzyme names typically end in –ase.
Hydrolases derive their names from substrates (e.g., urease from urea).
Page 11: Examples of Enzymes
Unique Nomenclature
Some enzymes named based on substrate and catalyzed reaction (e.g., lactate dehydrogenase).
Others have historical names with no direct relationship to substrate (e.g., catalase, pepsin).
Page 12: Effect of Enzymes on Activation Energy
Mechanism
Enzymes catalyze reactions by lowering activation energy, facilitating conversion of substrates to products.
Equilibrium constant (Keq) reflects the energy differences between reactants and products.
Page 13: Energy Difference Diagram
Comparison
Uncatalyzed reactions exhibit high activation energy, while catalyzed reactions show significantly reduced activation energy, leading to increased reaction rates.
Page 14: Substrate Concentration Impact
Reaction Dynamics
Uncatalyzed reaction rates increase with substrate concentration.
Enzyme-catalyzed reactions show two stages: formation of enzyme-substrate complex and slow conversion to product.
Page 15: Enzyme-Substrate Complex
Reaction Steps
Steps in an enzyme-catalyzed reaction: formation of enzyme-substrate complex (E-S), transition state (E-S*), and enzyme-product complex (E-P).
Page 16: Active Site Details
Characteristics
The active site is the region where the substrate interacts with the enzyme, characterized by:
Pockets or clefts on the enzyme surface.
Catalytic groups interact with substrate through weak noncovalent interactions.
Specificity is determined by the conformation of the active site.
Page 17: Lock-and-Key Model
Model Description
The enzyme (lock) and substrate (key) must fit exactly. However, this model does not account for conformational changes of enzymes during substrate binding.
Page 18: Induced-Fit Model
Flexible Pocket
The induced-fit model accounts for a flexible enzyme active site that adapts to accommodate the substrate molecule.
Page 19: Enzyme-Substrate Specificity
Compatibility
For a reaction to occur, the enzyme and substrate surfaces must be complementary, emphasizing enzyme specificity.
Example: Urease exhibits a high degree of specificity.
Page 20: Classes of Enzyme Specificity
Types of Specificity
Absolute: Reacts with only one substrate.
Group: Catalyzes reactions with similar functional groups.
Linkage: Catalyzes formation/breaking of specific bond types.
Stereochemical: Recognizes one of two enantiomers.
Page 21: Transition State and Product Formation
Function of Enzymes
Enzymes promote faster reactions by facilitating a transition state that is less stable and breaks down into product, which dissociates from the enzyme.
Page 22: Transition State Change 1
Bond Facilitating
Enzymes may exert "stress" on bonds, promoting bond breakage.
Page 23: Transition State Change 2
Proper Orientation
Enzymes bring two reactants into close proximity and proper orientation, increasing reaction likelihood.
Page 24: Transition State Change 3
pH Modification
Enzymes can alter pH in their microenvironment, facilitating reactions by donating or accepting H+ ions.
Page 25: Cofactors and Coenzymes
Definitions
Active enzyme/Holoenzyme: Consists of the polypeptide portion (apoenzyme) plus a nonprotein group (cofactor).
Cofactors maintain the active site configuration, including metal ions and organometallic compounds.
Page 26: Cofactor Representation
Visual Concept
Illustrates that the absence of a cofactor results in no enzyme-substrate complex formation, while its presence allows the reaction to proceed.
Page 27: Coenzymes
Characteristics
Coenzymes are organic molecules needed by some enzymes, usually carrying electrons or groups and often derived from vitamins.
Page 28: Water-Soluble Vitamins and Coenzymes
Table Overview
Lists various water-soluble vitamins and their coenzymes, alongside their key functions and roles in enzymatic reactions.
Page 29: NAD Mechanism
Functionality
The nicotinamide part of NAD+ accepts a hydride ion during oxidation processes, essential for various enzymatic reactions.
Page 30: Other Adenine Dinucleotide Coenzymes
Examples
Describes NADP+ and FAD as important coenzymes involved in oxidation/reduction reactions in metabolic processes.
Page 31: Environmental Effects on Enzymes
pH Impact
Enzymes function optimally within a specific pH range; extremes can denature them, impairing catalysis (e.g., pepsin in low pH, trypsin in high pH).
Page 32: Temperature Effects
Overview
Each enzyme has a temperature optimum for maximal function; excessive heat can lead to denaturation, resulting in loss of activity.
Page 33: Regulation of Enzyme Activity
Regulatory Methods
Enzymes differ from nonbiological catalysts by their regulation mechanisms:
Enzyme production in the presence of substrates.
Allosteric regulation.
Feedback inhibition.
Synthesis of proenzymes.
Protein modification.
Page 34: Allosteric Enzymes
Functionality
Allosteric regulation occurs when effector molecules bind to second sites, thereby altering the active site configuration.
Positive and negative allosterism regulates enzyme activity.
Page 35: Allosteric Regulation in Metabolism
Example
In glycolysis, ATP acts as a negative effector, while AMP acts as a positive effector for the enzyme phosphofructokinase, influencing metabolic pathways.
Page 36: Feedback Inhibition
Mechanism
Feedback inhibition utilizes allosteric enzymes where late products inhibit earlier pathways, preventing overproduction of intermediates.
Page 37: Proenzymes
Overview
Proenzymes are inactive enzymes activated by proteolysis when needed, such as pepsinogen converting to pepsin in the stomach.
Page 38: Digestive Tract Proenzymes
Specifics Table
Lists various digestive proenzymes and their corresponding activators, showcasing the specificity of activation processes.
Page 39: Protein Modification
Covalent Changes
Chemical modifications such as phosphorylation can activate or inhibit enzyme functions depending on situational needs.
Page 40: Inhibition of Enzyme Activity
Classification
Inhibitors can be classified as irreversible, which bind permanently to enzymes, or reversible, which compete with substrates for binding to the active site.
Page 41: Irreversible Inhibitors
Characteristics
Irreversible inhibitors bind tightly and can block active sites or interfere with the enzyme's catalytic activity.
Examples: arsenic, snake venom, nerve gas.
Page 42: Reversible, Competitive Inhibitors
Mechanism
Reversible inhibitors resemble substrates and compete for the active site, inhibiting enzyme activity depending on their concentrations relative to those of substrates.
Page 43: Representation of Competitive Inhibition
Visual Overview
Illustrative model showing how competitive inhibitors occupy active sites to prevent enzyme activity while substrates compete for the same position.
Page 44: Uses of Enzymes in Medicine
Diagnostic Applications
Enzymes serve as biomarkers for diseases such as acute myocardial infarction and pancreatitis, with specific enzymes indicating particular health issues.