Microsomal Enzyme Inhibition & Enzyme Inhibitors (Pharmacokinetics Part 11) by Dr. Shikha Parmar
An enzyme inhibitor is a molecule that binds to an enzyme and decreases its activity. The binding of an inhibitor can stop a substrate from entering the enzyme's active site and/or hinder the enzyme from catalyzing its reaction. Inhibitor binding is either reversible or irreversible. Irreversible inhibitors usually react with the enzyme and change it chemically (e.g. via covalent bond formation). These inhibitors modify key amino acid residues needed for enzymatic activity. In contrast, reversible inhibitors bind non-covalently and different types of inhibition are produced depending on whether these inhibitors bind to the enzyme, the enzyme-substrate complex, or both.
Many drug molecules are enzyme inhibitors, so their discovery and improvement is an active area of research in biochemistry and pharmacology. A medicinal enzyme inhibitor is often judged by its specificity (its lack of binding to other proteins) and its potency (its dissociation constant, which indicates the concentration needed to inhibit the enzyme). High specificity and potency ensure that a drug will have few side effects and thus low toxicity.
Competitive inhibitors compete for the substrate-binding site of the enzyme with the substrate because of the substrate and the inhibitor bind to identical or overlapping sites. Due to the overlapping nature of the binding sites, a ternary complex—in which the substrate and the inhibitor would simultaneously bind to the enzyme—can not form. Accordingly, in the enzyme-inhibitor complex, the enzyme is completely inactive.
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