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Questions and Answers
Which of the following is NOT a characteristic that differentiates isoenzymes?
Which of the following is NOT a characteristic that differentiates isoenzymes?
How many isoenzymes are present in lactate dehydrogenase?
How many isoenzymes are present in lactate dehydrogenase?
Which type of regulation involves feedback methods?
Which type of regulation involves feedback methods?
What can an elevation of plasma enzyme activity indicate?
What can an elevation of plasma enzyme activity indicate?
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What is the purpose of measuring alanine aminotransferase (ALT) levels?
What is the purpose of measuring alanine aminotransferase (ALT) levels?
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What is the primary effect of competitive inhibitors on enzyme kinetics?
What is the primary effect of competitive inhibitors on enzyme kinetics?
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Which type of inhibitor binds covalently or very tightly to the enzyme, leading to irreversible inactivation?
Which type of inhibitor binds covalently or very tightly to the enzyme, leading to irreversible inactivation?
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What is the typical characteristic of noncompetitive inhibitors regarding Km and Vmax?
What is the typical characteristic of noncompetitive inhibitors regarding Km and Vmax?
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What is the role of allosteric sites in allosteric enzymes?
What is the role of allosteric sites in allosteric enzymes?
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Which of the following is an example of a competitive inhibitor?
Which of the following is an example of a competitive inhibitor?
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What kind of inhibitors do not resemble the substrate and bind at a different site?
What kind of inhibitors do not resemble the substrate and bind at a different site?
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What effect do competitive inhibitors have on substrate concentration in overcoming inhibition?
What effect do competitive inhibitors have on substrate concentration in overcoming inhibition?
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Which enzyme is inhibited by cyanide?
Which enzyme is inhibited by cyanide?
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Study Notes
Enzyme Inhibition
- Enzyme inhibitors are compounds that reduce the speed of an enzyme-catalyzed reaction by binding to the enzyme.
- Two main types of enzyme inhibitors exist: reversible and irreversible inhibitors.
Reversible Inhibitors
- These inhibitors bind non-covalently to the enzyme, allowing for dissociation.
- Subcategories of reversible inhibitors include competitive inhibitors.
Competitive Inhibitors
- Competitive inhibitors compete with the substrate for binding to the enzyme's active site.
- These inhibitors generally resemble the substrate in structure.
- Increasing substrate concentration can overcome competitive inhibition.
- Competitive inhibition increases the KM value, but does not alter Vmax.
- Methotrexate is an example of a competitive inhibitor, which is an anticancer drug that inhibits the enzyme dihydrofolate reductase.
Non-competitive Inhibitors
- Non-competitive inhibitors bind to a site on the enzyme other than the active site, affecting the enzyme's ability to function.
- Non-competitive inhibitors do not resemble the substrate.
- Non-competitive binding reduces Vmax, but does not affect KM.
- Cyanide is an example of a non-competitive inhibitor, which inhibits the enzyme cytochrome oxidase.
Irreversible Inhibitors
- Irreversible inhibitors bind covalently or very tightly to the enzyme's active site, permanently inactivating it.
Allosteric Enzymes
- Allosteric enzymes have multiple binding sites, including regulatory sites.
- These sites can bind activators or inhibitors, affecting enzyme activity.
- Allosteric enzymes are often involved in the initial steps of metabolic pathways and frequently catalyze irreversible reactions.
Isoenzymes
- Isoenzymes are enzymes that catalyze the same reaction but have different structures.
- Isoenzymes vary in their structure and their affinity for the substrate.
- Isoenzymes exhibit variations in their resistance to inhibitors and mobility in electrical fields (electrophoresis).
- Lactate dehydrogenase (LDH) is an example, with five distinct isoenzymes having different subunit compositions.
Regulation of Enzyme Activity
- Allosteric regulation involves feedback and feed-forward mechanisms.
- Covalent modification, including phosphorylation and dephosphorylation, also regulates enzyme activity.
Enzymes in Clinical Diagnosis
- Elevated enzyme activity in the blood may indicate tissue damage, which is frequently useful in diagnosis and prognosis.
- Plasma enzymes are sensitive indicators of tissue damage or disease.
- Alanine aminotransferase (ALT) levels can indicate liver damage when elevated.
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Description
Explore the fascinating world of enzyme inhibition, focusing on both reversible and irreversible inhibitors. Learn about competitive and non-competitive inhibitors, their mechanisms, and examples of their applications in medicine. Understand how these inhibitors affect enzyme activity and the implications for various biological processes.
