Enzymes and Coenzymes (2) PDF

Enzymes and Coenzymes (2) Editing File Color Index: - Main Text (black) - Female Slides (Pink) - Male Slides (Blue) - Important (Red) - Dr’s Notes (Green) - Extra Inf...

Enzymes and Coenzymes (2) Editing File Color Index: - Main Text (black) - Female Slides (Pink) - Male Slides (Blue) - Important (Red) - Dr’s Notes (Green) - Extra Info (Grey)  Objectives Understand the enzyme kinetics, types of inhibition and regulation of enzyme activity. Discuss the clinical role enzymes in the diagnosis of diseases. Enzyme Inhibitions Inhibitions is the process by which the enzyme activity is regulated or controlled or stopped. To inhibit means to stop the enzyme activity. (the inhibition might be 100% or partial) An enzyme without inhibitor Enzymes Inhibitions An enzyme with inhibitor Competitive Noncompetitive Uncompetitive Inhibitor constant Kᵢ Ki is a measure of the affinity of the inhibitor for the enzyme. Also known as dissociation constant. Not to be confused with Km Affinity means attraction. Km means the substrate Here we mean the attraction of concentration that is needed to the substrate to the enzyme. achieve one-half of the maximum rate (½ Vmax) Competitive inhibition Helpful video 1 The inhibitor is a structural analogue (similar) that competes with the substrate for binding at the active site of enzyme 2 Two equilibria/reactions are possible: E : Enzyme E+S ES E+P S : Substrate and P : Product ES : enzyme-substrate complex E+I EI I : Inhibitor 3 The value of Vmax is unchanged in the presence and the absence of inhibitor 4 The value of Km is increased because substrate and inhibitor compete for Enzyme can bind to binding at the same site (Active site). substrate or the inhibitor 5 A higher [S] is required to achieve ½ Vmax. depending on which one has more affinity to the enzyme.  Competitive inhibition The value of Vmax is unchanged Maximal velocity Vmax is the same in the presence of a competitive inhibitors ½ Vₘₐₓ The value of Km is increased Michaelis constant Km is apparently increased in the presence of a competitive inhibitors Noncompetitive inhibition Helpful video 1 The inhibitor does not have structural similarity to the substrate. 2 The inhibitor binds to the enzyme at a site away from the substrate binding site. (at Allosteric site) 3 No competition exists between the inhibitor and the substrate. The inhibitor can bind to a free enzyme or to an enzyme-substrate 4 complex ES + I ESI (Inactive) In both cases the complex and is catalytically inactive when the noncompetitive E+I EI (Inactive) inhibitor bind to the allosteric site it will change the shape of the active site which will 5 The value of Vmax is decreased by the inhibitor, but Km is unchanged prevent the substrate from binding. because the affinity of S for E is unchanged. ( it can control the active site (because substrate and inhibitor aren’t competing for the same site). positively or negatively)  Noncompetitive inhibition Maximal velocity Vmax is apparently decreased in the presence of non-competitive inhibitors The value of Vmax is decreasing Michaelis constant Km is The value of Km unchanged in the presence of is unchanged a non-competitive inhibitors  Helpful video Quick Comparing Competitive Non-Competitive Structure Similar to the substrate Dissimilar to the substrate Binding site Active Site Allosteric Site Competition Exists Nonexistent E + S ⇔ ES ⇒ E + P ES + I ⇔ ESI Reactions E + I ⇒ EI E + I ⇔ EI Maximal velocity Unchanged Decreased Vmax Michaelis Increased Unchanged constant Km Competitive and Noncompetitive inhibition Regulation of enzyme activity Regulatory (regulation can be activating or inhibiting) enzymes usually catalyze the first or an early reaction in a metabolic pathway. (The earliest it’s stopped the best) They catalyze a rate limiting reaction that controls the overall pathway. (It requires energy ) They may also catalyze a reaction unique to that pathway known as committed step. Med39: Enzymes control the overall pathway by utilizing or giving energy.  Feedback inhibition Feed positive (Negative) activation When the end product of a When the end product of metabolic pathway a metabolic pathway is exceeds its concentration below its concentration limit, it inhibits the limit, it activates the regulatory enzyme to regulatory enzyme to normalize the pathway. normalize the pathway. (feedback inhibition) Med439: Cells use feedback inhibition to slow down the production, conserve energy and to maintain a state of homeostasis. e.g. If you have enough of product E you can't stop enzyme 1 because you will affect enzyme 5 so the first committed step is stopping enzyme 2 Types of regulation Allosteric enzyme regulation: (Non-Competitive) Helpful video until 1:12 The enzymes in metabolic pathways whose activities can be regulated by certain compounds(Ligand or modulator) that bind to enzyme other than the catalytic site are known as allosteric enzymes. These ligands do not bind to active site. They bind to another site (regulatory/allosteric site) on the enzyme(allosteric enzyme). The term “ allosteric ” came from Greek word “ allos ” meaning “other”. Most allosteric enzymes are oligomers (two or more polypeptide chains or subunits). The subunits are known as protomers. The effect of a modulator (ligands) may be Positive(activation) OR Negative(inhibition). increased E, S affinity Decreased E, S affinity  Allosteric Inhibition Allosteric Activation The active site becomes The active site unavailable to the becomes available to substrates when a the substrates when a regulatory molecule regulatory molecule binds to a different site binds to a different site on the enzyme. on the enzyme. Allosteric enzymes Interactions Heterotropic Homotropic Effect of one ligand on the binding of Effect of one ligand on the same ligand the binding of a (a regulatory enzyme modulated by different ligand its own substrate) Types of regulation Cooperative binding: Helpful video The process by which binding of a ligand to a regulatory site affects binding of the same(Homotropic) or of another(Heterotropic) ligand to the enzyme. This is called Cooperative Binding. Binding of an allosteric modulator (ligand) causes a change in the conformation/active site of the enzyme. This causes a change in the binding affinity of enzyme for the substrate. Enzymatic diagnosis and prognosis of diseases Enzymes are used clinically in three ways: - As indicators of enzyme activity or conc. in body fluids (serum, urine) in the diagnosis/prognosis of diseases. - As analytical reagents in measuring activity of other enzymes or compounds in body fluids. - As therapeutic agents. Plasma and Serum are The most commonly used body fluids for measuring enzyme activity. There is: Serum markers in the diagnosis of diseases: -Plasma-specific enzymes (present - Heart disease (troponin) in blood) - Pancreatic diseases (Lipase and amylase) – Non Plasma-specific enzymes - Liver diseases (ALT & AST) You don’t need to memorise these enzymes  Take Home Messages o Enzymes are essential for all biochemical reactions in the body. o A number of diseases are treated by inhibiting specific enzymes. o Many enzymes are used as biomarkers for diagnosis of diseases.  Question 1 Which one of the following types of inhibitors requires more substrate to reach ½ Vmax? A Non-Competitive C All of them B Competitive D None of them  Question 1 Which one of the following types of inhibitors requires more substrate to reach ½ Vmax? A Non-Competitive C All of them B Competitive D None of them  Question 2 Which of these mechanisms increases the km: Competitive Competitive A inhibition C activation Non-competitive Non-competitive B inhibition D activation  Question 2 Which of these mechanisms increases the km: Competitive Competitive A inhibition C activation Non-competitive Non-competitive B inhibition D activation  Question 3 Known as dissociation constant : A Vmax C Km B [S] D Ki  Question 3 Known as dissociation constant : A Vmax C Km B [S] D Ki  Question 4 What happens to Vmax in the case of non-competitive inhibition? A Decreased C Stay the same B Increased D All of them  Question 4 What happens to Vmax in the case of non-competitive inhibition? A Decreased C Stay the same B Increased D All of them  Question 5 Most allosteric enzymes are : A Monomers C Protomers B Oligomers D Enantiomers  Question 5 Most allosteric enzymes are : A Monomers C Protomers B Oligomers D Enantiomers  Question 6 The effect of a positive modulator : A Increase E,S affinity C Decreased E,S affinity Increased E and Decreased E and B Decreased S affinity D increased S affinity  Question 6 The effect of a positive modulator : A Increase E,S affinity C Decreased E,S affinity Increased E and Decreased E and B Decreased S affinity D increased S affinity  SAQ Question 1 1) What kind of inhibition is seen in the diagram? 1) How does it affect Vmax ? 1) How does it affect in Km 1) Non-competitive inhibition 2) Decreases it 3) It doesn’t change because the affinity of S for E is unchanged (because the substrate and inhibitor aren’t competing for the same site).  SAQ Question 2 1) What kind of inhibition is seen in the diagram? 1) How does it affect Vmax ? 1) How does it affect in Km? 1) Competitive inhibition 2) It doesn’t change 3) Increases it because the substrate and the inhibitor compete for bending to the same site  SAQ Question 3 Which type of feedback occurs when the metabolic pathway is below it’s concentration limit? Feed positive activation  SAQ Question 4 In which diseases can you use enzymes as a markers? Heart disease - Pancreatic disease - Liver disease  Biochemistry Team Alanoud Yasser Almutairi Lura Almusaeeb Alnajawi Ahmad Addas Hossam Alhussain Ghala Alyousef Shaden Alotaibi Faisal Alomran Abdullah Alzoom Huda Bassam Aljawharah Alyahya Abdulrahman Almalki Ziyad Alenazi Manar Alqahtani Norah Albahdal Ziyad Bukhari Tariq Alshumrani Marwa Fal Ghaida Alotaibi Talal Alrobaian Mohammed Almurshid Jenan Al-Sayari Ghida Alkahtani Essam Nawaf Abdullah Almutlaq Rahaf Aldawood Lama Alhayan Team Med444 Mays Altokhais Shaden Alshammari