7.12
Enzymhemmung
Inhibitoren sind Moleküle, welche die Enzymaktivität durch die Bindung des Enzyms hemmen. In einer normal funktionierenden Zelle werden die Enzyme dur…
Spezifische Chemikalien steuern die Wirkung von Enzymen, durch Hemmung oder Blockierung ihrer Funktion. Enzymhemmer gibt es in zwei verschiedenen Formen, konkurrierend und nicht konkurrierend. Ein konkurrierender Hemmer ist dem spezifischen Substrat des Enzyms so ähnlich, dass er an die aktive Stelle binden kann und das Substrat von der Bindung abhält.
Diese Aktion verringert die Zahl der Enzyme erheblich, die für die Bindung an das Substrat zur Verfügung stehen. Im Gegensatz dazu bindet ein nicht konkurrierender Hemmer sich von der aktiven Stelle weg, beeinflusst sie aber, indem er z. B. die Form des Enzyms ändert und die Affinität für die Substratbindung an die aktive Stelle stark reduziert und verhindert, dass das Enzym ordnungsgemäß funktioniert.
Darüber hinaus beeinflussen beide Inhibitortypen die Geschwindigkeit einer chemischen Reaktion unterschiedlich. Im Vergleich zu einer Kontrolle, einer normalen enzymatischen Reaktionsgeschwindigkeit, würde eine Reaktion mit einem konkurrierenden Hemmer länger dauern, um v max, die maximale Reaktionsgeschwindigkeit, zu erreichen, und würde mehr Substrat erfordern, um dies zu tun, da es genügend Substrat geben muss, um den Hemmer konsequent um den Zugang zu den aktiven Stellen zu übertreffen. Andererseits würde ein nicht konkurrierender Inhibitor nicht zulassen, dass die Rate v max erreicht, da die Anzahl der für die Bindung verfügbaren Enzyme reduziert wird.
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Q1: What is the difference between competitive and non-competitive enzyme inhibitors?
Competitive inhibitors resemble the enzyme's substrate and bind to the active site, blocking substrate access and reducing available enzymes. Non-competitive inhibitors bind to allosteric sites away from the active site, changing the enzyme's shape and reducing substrate affinity. Both types regulate enzyme function but through different mechanisms and with distinct effects on reaction rates.
Q2: How does a competitive inhibitor affect the maximum reaction rate?
A competitive inhibitor does not prevent the enzyme from reaching Vmax, the maximum reaction rate. However, it requires more substrate and longer time to achieve this rate because substrate must outcompete the inhibitor for active site access. With sufficiently high substrate concentrations, the enzyme can still reach its maximum velocity.
Q3: Why can't non-competitive inhibitors be overcome by increasing substrate concentration?
Non-competitive inhibitors bind to allosteric sites and reduce the total number of functional enzymes available. Since they don't occupy the active site, adding more substrate cannot overcome their effect. The enzyme cannot achieve Vmax because the inhibitor permanently reduces the enzyme population capable of catalyzing the reaction.
Q4: What is an example of a competitive inhibitor used as a drug?
Disulfiram is a competitive inhibitor used to treat chronic alcoholism. It binds to the active site of acetaldehyde dehydrogenase, preventing the conversion of acetaldehyde to acetyl coenzyme A. When alcohol is ingested, acetaldehyde accumulates, causing hangover-like symptoms that discourage alcohol consumption.
Q5: How do reversible and irreversible enzyme inhibitors differ in cells?
Reversible inhibitors interact with enzymes through weak interactions and are useful for regulating metabolic processes in normally functioning cells. Irreversible inhibitors form covalent bonds with enzymes, permanently blocking their function. Some toxins use irreversible inhibition, while regulatory inhibitors typically employ reversible binding for metabolic control.
Q6: How do enzyme inhibitors regulate cellular metabolism?
Inhibitors reduce enzyme activity by binding to the enzyme, either at the active site or at allosteric sites. This regulation allows cells to control reaction rates and metabolic pathways. Drugs and toxins can also inhibit enzymes, making inhibition a critical mechanism for both normal cellular function and therapeutic intervention.
Q7: Why are enzyme inhibitors important targets for cancer research?
Cancer cells rely on enzymes regulating cell growth and division. Researchers explore molecules that competitively and non-competitively inhibit these growth-regulating enzymes to block cancer cell proliferation. By targeting specific enzymes with inhibitors, scientists can develop therapies that selectively suppress cancer cell activity while minimizing effects on normal cells.