Types of Enzyme Inhibitors
An enzyme inhibitors is a molecule that attaches to an enzyme, blocking its activity. Enzymes are proteins that speed up chemical reactions required for life. These reactions convert substrate molecules into products. Enzyme inhibition is used to block the activity of these enzymes. Let’s take a closer look at each type. Which type is right for you? Here are the three main types of enzyme inhibitors. You can learn about them in this article.
The simplest model of reversible inhibitory activity involves direct occlusion of the active site by a molecule with structural similarity to the substrate. In competitive inhibition, the inhibitor and substrate have mutually exclusive binding. This results in an increasing slope of the plot. In some cases, this can result in a decreasing Vmax. In the following discussion, we will discuss both competitive and noncompetitive inhibition.
Competitive inhibition involves the use of a chemical that interferes with the activity of an enzyme by increasing the size of the substrate. On the other hand, noncompetitive inhibition involves using a compound that decreases the amount of substrate required to achieve saturation. The two models of enzyme inhibition differ in how they analyze inhibitor kinetic data, but they both involve the same principles. Both models involve analysis of inhibition kinetic data, with a Lineweaver-Burk plot indicating the rate of enzyme reversibility.
Reversible inhibition involves chemical inhibitors that bind to the active center of an enzyme through non-covalent interactions. These inhibitors bind to remnants of the enzyme’s active center, blocking the formation of an enzyme-substrate complex. It takes a long time for the complex to dissociate. As a result, irreversible inhibition requires a long period to restore. This is because irreversible inhibition is not competitive.
Competitive inhibitors bind to an enzyme’s active site and are highly effective in inhibiting enzyme activity. They covalently modify the enzyme’s active site, but they don’t change its structure. This means that the inhibition will remain even if the enzyme is exposed to excess substrate. Moreover, these inhibitors are less expensive than competitive inhibitors. However, they are more effective than irreversible inhibitors. So, they are generally preferable when reversible inhibitors are used in clinical settings.
Suicide inhibition is a different type of inhibitory action. Suicide inhibitors bind to the enzyme covalently and cannot be removed from the enzyme. This type of inhibition is similar to competitive inhibition. It is used to prevent the synthesis of many amino acids. For example, bacteria synthesize isoleucine from threonine through five enzyme-catalyzed steps. As a result, isoleucine binds to the first enzyme and inhibits its activity.
There are two kinds of competitive inhibition: irreversible and reversible. In the first case, the inhibitor can be overcome by increasing the concentration of its target, while in the latter, the enzyme must produce more of the substrate or degrade it to excrete it. Another type of competitive inhibition is allosteric. Here, the inhibitor and substrate cannot bind to the enzyme simultaneously. However, allosteric inhibition is not as common as competitive inhibition.
In contrast, noncompetitive inhibition is the opposite of competitive inhibition. In this form, an enzyme is inactive when a molecule that is not its natural substrate binds to its active site. The competitive inhibitor prevents the natural substrate from binding to the enzyme and suppresses its activity. Both types of inhibition are different and obey Michaelis-Menten kinetics. When both substrate and inhibitor are present, competitive inhibition inactivates the enzyme.
Competitive inhibition has many applications. For example, acetazolamide inhibits carbonic anhydrase, Viagra and Levitra inhibit phosphodiesterases, and efavirenz and nevirapine suppress HIV reverse transcriptase. Competitive inhibitors change the Km and Vmax of the enzyme. This effect is beneficial for determining which enzymes are active in specific tissues and conditions. However, it is essential to note that competitive inhibition has several limitations.
The most prominent disadvantage of competitive inhibition is that both inhibitors affect the same site on the enzyme. This type of inhibition has a detrimental effect on drug efficacy. This is because competitive inhibitors reduce substrate concentration in the active site, while non-competitive inhibitors inhibit the same area of the enzyme. Despite the similarities between the two inhibitor types, each affects the same enzyme differently. Nonetheless, competitive inhibitors are more effective than noncompetitive inhibitors.
Noncompetitive inhibitors compete with the enzyme at a different location than its substrate. They decrease Vmax without altering the Michaelis constant. As a result, they cannot be reversed by increasing the substrate concentration. The graph plotting enzyme activity versus substrate concentration would have a lower Vmax value and a steeper Lineweaver-Burke curve. The plot would remain unchanged if there were no inhibitors.
In chemical reactions, the inhibitor can bind to the enzyme either as a free molecule or complex with the enzyme’s substrate. This type of inhibition is considered a conceptual combination of competitive and noncompetitive inhibition. It often occurs in reactions with multiple substrates. During the reaction, the enzyme cannot produce the product required. For this reason, this type of inhibition is usually called mixed inhibition. Here are the differences between these two types of inhibition.
Competitive inhibitors compete for the enzyme’s binding site, while mixed inhibitors bind to the free and enzyme-substrate complex. In contrast, irreversible inhibitors are helpful for therapeutic purposes, but their binding is difficult to monitor because the enzyme binds only to its substrate. In the case of competitive inhibitors, they are complicated to measure and use because they do not completely inhibit the enzyme. However, irreversible inhibitors are sometimes used to induce reversible changes in the enzyme’s structure.
Simulation results showed that the inhibitor had a catalytic and allosteric effect on the PTP1B enzyme. The inhibitor binds with the PTP1B allosteric site, resulting in -8.24 kcal/mol binding energy. In addition, three hydrogen bonds were observed between residues in the inhibitor and PTP1B, with bond distances of 2.73 A between Tyr152 and Phe196.
To determine whether the mixed type inhibitors effectively inhibit the PTP1B enzyme, we performed a kinetic assay. We used sEH, bisisomahanine, and tyrosine to determine their ability to inhibit a-glucosidase (PTP1B). For comparison, we also tested the inhibitors against a-glucosidase and PTP1A and PTP1B, using different concentrations of these two substrates.
The DX600-induced inhibition of ACE2 is a specific inhibitor of ACE2, a crucial component of the renin-angiotensin system. It modulates its adverse effects as an integral component of the ACE/ANG II/AT1 receptor axis. Using the active site of ACE2 as a measure of its compensatory function requires a more accurate estimate and a thorough understanding of species-specific differences.
The mechanism of enzyme inhibition is complex, involving the competition of inhibitor molecules with the standard substrate for binding to the active site. Inhibitor molecules are structural analogs of the substrate, and forming an E-I complex limits the number of enzyme molecules available for E-S formation. For example, a hundred substrate molecules compete for the same active site, with half of the enzyme trapped by the inhibitor. As a result, only half of the enzyme molecules are available for catalysis to generate the desired product.
The rate constants for ES and E are the same, but the specificity of the inhibitor is different. The slope of the Lineweaver-Burk plot is the same for both cases, suggesting that the inhibitor competes for binding to E. As a result, the productivity of the enzyme is unchanged. However, in mixed inhibition, the substrate and inhibitor have different effects. Therefore, a mixture of inhibition mechanisms is often used.
There are two kinds of inhibitors: competitive and noncompetitive. Competitive inhibition blocks the enzyme’s active site by competing with the natural substrate. In this case, the inhibitor attaches to the enzyme at an allosteric site. The enzyme cannot split the inhibitor, thus inhibiting the reaction. On the other hand, noncompetitive inhibition is where an inhibitor binds to an enzyme but does not compete with its natural substrate for the active site. This inhibits the reaction by combining with the enzyme-substrate complex.
Artificial molecular clips and tweezers, or artificial molecular clips and tweezing agents, have been developed to inhibit various enzymes. For example, artificial molecular clips and tweezers dock onto the lysine residues around the active site. These techniques can be partially reversed by adding appropriate additives. NAD+ can restore cofactor levels. Furthermore, it may lead to novel techniques for inhibitory drugs.
There are many types of inhibitors. In general, enzyme inhibitors can be divided into three types: competitive inhibitors and uncompetitive inhibitors. Competitive inhibitors bind to the enzyme’s active site and keep it functional, while non-competitive inhibitors bind to the enzyme alone. They also play a role in biochemical pathways. Inhibitors are helpful in drug discovery, drug development, and biochemical pathway studies.