Enzymes are the workhorses of our cells, speeding up reactions. But they need control. This section dives into how cells regulate enzymes through inhibition and other mechanisms, keeping our biochemical processes in check.
We'll explore different types of enzyme inhibition, from competitive to irreversible. We'll also look at regulation methods like allosteric control and covalent changes. Understanding these helps us grasp how cells fine-tune their chemistry.
Enzyme Inhibition Types
Competitive and Noncompetitive Inhibition
Top images from around the web for Competitive and Noncompetitive Inhibition
Competitive inhibition - Wikipedia View original
Is this image relevant?
Energy, Matter, and Enzymes · Microbiology View original
Is this image relevant?
Enzymes | Boundless Biology View original
Is this image relevant?
Competitive inhibition - Wikipedia View original
Is this image relevant?
Energy, Matter, and Enzymes · Microbiology View original
Is this image relevant?
1 of 3
Top images from around the web for Competitive and Noncompetitive Inhibition
Competitive inhibition - Wikipedia View original
Is this image relevant?
Energy, Matter, and Enzymes · Microbiology View original
Is this image relevant?
Enzymes | Boundless Biology View original
Is this image relevant?
Competitive inhibition - Wikipedia View original
Is this image relevant?
Energy, Matter, and Enzymes · Microbiology View original
Is this image relevant?
1 of 3
- Competitive inhibition occurs when inhibitor molecules bind to enzyme's active site
- Inhibitors structurally resemble substrate molecules
- Compete with substrates for binding to active site
- Decreases apparent affinity of enzyme for substrate
- Can be overcome by increasing substrate concentration
- Noncompetitive inhibition involves inhibitor binding to allosteric site
- Allosteric site located away from active site
- Binding causes conformational change in enzyme
- Reduces enzyme's catalytic activity
- Cannot be overcome by increasing substrate concentration
- Kinetic differences between competitive and noncompetitive inhibition
- Competitive inhibition affects Km (Michaelis constant) but not Vmax
- Noncompetitive inhibition affects Vmax but not Km
- Examples of competitive inhibitors include sulfa drugs (antibiotics)
- Examples of noncompetitive inhibitors include heavy metals (mercury, lead)
Uncompetitive and Reversible Inhibition
- Uncompetitive inhibition involves inhibitor binding only to enzyme-substrate complex
- Prevents product formation
- Decreases both Km and Vmax
- Rare in nature but important in drug design
- Reversible inhibition allows inhibitor to dissociate from enzyme
- Enzyme activity can be restored
- Includes competitive, noncompetitive, and uncompetitive inhibition
- Inhibition strength depends on inhibitor concentration
- Ki (inhibition constant) measures inhibitor's affinity for enzyme
- Smaller Ki indicates stronger inhibition
- Used to compare effectiveness of different inhibitors
- Calculated using enzyme kinetics experiments
- Examples of uncompetitive inhibitors include methotrexate (cancer treatment)
- Examples of reversible inhibitors include acetylcholinesterase inhibitors (Alzheimer's treatment)
Irreversible Inhibition and Enzyme Inactivation
- Irreversible inhibition permanently inactivates enzyme
- Inhibitor forms covalent bond with enzyme
- Often targets specific amino acid residues in active site
- Enzyme activity cannot be restored
- Mechanism-based inhibitors (suicide inhibitors)
- Initially bind as substrates
- Enzyme converts inhibitor to reactive intermediate
- Reactive intermediate forms covalent bond with enzyme
- Irreversible inhibitors often used as drugs or pesticides
- Require lower doses than reversible inhibitors
- Can have long-lasting effects
- Examples of irreversible inhibitors include aspirin (COX inhibitor) and organophosphates (nerve agents)
Enzyme Regulation Mechanisms
Allosteric Regulation and Feedback Inhibition
- Allosteric regulation involves binding of effector molecules to allosteric sites
- Allosteric sites distinct from active site
- Effectors can be activators or inhibitors
- Binding causes conformational change in enzyme
- Alters enzyme's affinity for substrate or catalytic efficiency
- Cooperativity in allosteric enzymes
- Binding of one substrate molecule affects binding of subsequent molecules
- Positive cooperativity increases enzyme's affinity for substrate
- Negative cooperativity decreases enzyme's affinity for substrate
- Feedback inhibition regulates metabolic pathways
- End product of pathway inhibits earlier enzyme in pathway
- Prevents overproduction of metabolites
- Conserves energy and resources
- Examples of allosteric enzymes include hemoglobin (oxygen binding)
- Examples of feedback inhibition include cholesterol biosynthesis pathway
Covalent Modification and Zymogen Activation
- Covalent modification alters enzyme activity through chemical changes
- Common modifications include phosphorylation, acetylation, and methylation
- Enzymes responsible for modifications called kinases (phosphorylation)
- Enzymes removing modifications called phosphatases (dephosphorylation)
- Can activate or inhibit enzyme activity
- Allows rapid and reversible regulation
- Zymogen activation involves conversion of inactive precursor to active enzyme
- Zymogens (proenzymes) synthesized in inactive form
- Activation occurs through proteolytic cleavage
- Prevents premature enzyme activity
- Common in digestive enzymes and blood clotting factors
- Regulation of enzyme activity through protein-protein interactions
- Binding of regulatory proteins can activate or inhibit enzymes
- Allows integration of multiple signaling pathways
- Examples of covalent modification include glycogen metabolism (phosphorylation of glycogen synthase and phosphorylase)
- Examples of zymogens include trypsinogen (precursor to trypsin) and pepsinogen (precursor to pepsin)