Name: competitive vs noncompetitive inhibitors
Uploaded: 2025-10-23T11:48:34.000Z
Duration: 1 min 30 s
Channel: JoVE

- Produtos químicos específicos podem regular a ação das enzimas inibindo ou bloqueando sua função. 
Inibidores da enzima vêm em duas formas diferentes, competitivo e não competitivo. 
Um inibidor competitivo é semelhante o suficiente ao substrato específico da enzima que pode ligar-se ao sítio ativo, e impedir que o susbtrato se ligue. 
Essa ação essencialmente diminui o número de enzimas disponíveis para que o substrato se ligue. 
Em contraste, um inibidor não competitivo vai se ligar distante do sítio ativo, mas ainda influenciá-lo, mudando a forma da enzima, por exemplo, e reduzindo muito a afinidade para a ligação do substrato ao sítio ativo, impedindo que a enzima funcione corretamente. 
Além disso, ambos os tipos de inibidores afetam diferencialmente a taxa de uma reação química. 
Comparado a um controle, uma taxa de reação enzimática normal, uma reação incluindo um inibidor competitivo levaria mais tempo para atingir Vmax, a taxa máxima de reação, e exigiria mais substrato para isso, como deve haver substrato suficiente para consistentemente competir com o inibidor por acesso aos sítios ativos. 
Por outro lado, um inibidor não competitivo não permitiria que a taxa atingisse Vmax porque o número de enzimas disponíveis para ligação é reduzida.

Goh, Ee Teng e Marsha Y. Morgan. "Farmacoterapia para dependência de álcool - o porquê, o quê e o porquê." Farmacologia e Terapêutica Alimentar 45, nº 7 (2017): 865-882. [<a href="https://doi.org/10.1111/apt.13965">Fonte</a>]

inibição de enzimas

Enzyme Inhibition

Inibidores são moléculas que reduzem a atividade enzimática ligando-se à enzima. Em uma célula normalmente funcional, as enzimas são reguladas por uma variedade de inibidores. Fármacos e outras toxinas também podem inibir enzimas. Alguns inibidores ligam-se ao local ativo da enzima, enquanto que outros inibem a atividade enzimática ligando-se a outros locais na estrutura proteica.
 
 Inibidores competitivos ocupam o local ativo das enzimas, tornando-as incapazes de acomodar o substrato. No entanto, concentrações suficientemente altas do substrato podem superar o inibidor; como resultado, os inibidores competitivos retardam a velocidade de reação inicial das enzimas, mas não afetam a velocidade máxima da enzima. Um exemplo de inibidor competitivo é o fármaco dissulfiram, usado para tratar o alcoolismo crónico. Quando o álcool é ingerido, é normalmente convertido em acetaldeído, que é então convertido em acetil coenzima A pela acetaldeído desidrogenase. O dissulfiram liga-se e ocupa o local ativo da acetaldeído desidrogenase, tornando a enzima incapaz de realizar esta conversão. Como resultado, um paciente que toma dissulfiram começa imediatamente a experienciar sintomas semelhantes a ressaca, como dor de cabeça, diminuindo assim o consumo de álcool.
 
 Inibidores não competitivos ligam-se a locais distintos na enzima, longe do local ativo. Estes são chamados de locais alostéricos e quando as moléculas se ligam a eles, a forma do local ativo é alterada de tal maneira que a enzima fica com uma menor afinidade pelo substrato. Como os inibidores não competitivos não ocupam o local ativo, a presença de substrato adicional é incapaz de superar a inibição não competitiva e a enzima é incapaz de atingir sua velocidade máxima de reação.
 
 A ligação covalente entre um inibidor e uma enzima é geralmente irreversível, como no caso de algumas toxinas. A maioria dos inibidores regulatórios normalmente ativos na célula interagem com enzimas por interações fracas. Este tipo de ligação é reversível e útil para a regulação de processos metabólicos. O estudo de novas moléculas para inibir de forma competitiva e não competitiva enzimas que regulam o crescimento celular no cancro é uma área ativa de investigação.

Inibição de Enzimas

Inibidores são moléculas que reduzem a atividade enzimática ligando-se à enzima. Em uma célula que funciona normalmente, as enzimas são reguladas por uma variedade de ...

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competitive vs noncompetitive inhibitors

Enzyme inhibitors are molecules that reduce enzyme activity by binding to enzymes. Cells use these inhibitors to help regulate normal enzyme function. Drugs and toxins can also block enzymes and change how they work.

Some inhibitors bind at the active site, which is the part of the enzyme where the substrate normally fits. Competitive inhibitors do this by occupying the active site and preventing the substrate from binding. If the substrate concentration becomes high enough, it can outcompete the inhibitor. For that reason, competitive inhibitors slow the initial reaction rate but do not change the enzyme’s maximum rate.

A clear example is disulfiram, a drug used to treat chronic alcoholism. Alcohol is normally converted to acetaldehyde and then to acetyl coenzyme A by acetaldehyde dehydrogenase. Disulfiram binds to the active site of acetaldehyde dehydrogenase and blocks this conversion. This causes hangover-like symptoms, such as headache, and helps decrease alcohol consumption.

Noncompetitive inhibitors bind at a different part of the enzyme. These binding sites are called allosteric sites. When a noncompetitive inhibitor binds, it changes the shape of the active site and lowers the enzyme’s affinity for the substrate. Extra substrate cannot overcome this effect, so the enzyme cannot reach its maximum reaction rate.

Some inhibitors form covalent bonds with enzymes. This binding is usually irreversible, as with some toxins. Most inhibitors that regulate metabolism in cells bind more weakly. That weak binding is reversible and helps control metabolic processes. Researchers also study enzyme inhibitors as possible treatments for cancers that involve cell growth.

Competitive vs Noncompetitive Inhibitors

what is metabolism?

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Stored energy in motion and bonds is called potential energy. It depends on the structure of an object or the position of matter in space. Raising a kettlebell changes its location and increases its potential energy. A stretched rubber band also stores potential energy, which can later change into kinetic energy. Chemical bonds between atoms hold another form of stored energy called chemical energy. These bonds involve attractive forces, and that energy can change into other forms during a...

free energy

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enzyme kinetics

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Enzyme kinetics examines how enzymes change the rate of a reaction. Enzymes speed reactions by lowering the activation energy of the reactants. The reaction rate is the speed at which an enzyme turns reactants into products, and it can be affected by several factors, including the number of available reactants. Scientists often study enzyme kinetics in a test tube with a fixed amount of enzyme. When more substrate, or reactant, is added, the reaction rate increases because the enzyme can make...

enzyme inhibition

Enzyme inhibitors are molecules that reduce enzyme activity by binding to enzymes. Cells use these inhibitors to help regulate normal enzyme function. Drugs and toxins can also block enzymes and change how they work. Some inhibitors bind at the active site, which is the part of the enzyme where the substrate normally fits. Competitive inhibitors do this by occupying the active site and preventing the substrate from binding. If the substrate concentration becomes high enough, it can outcompete...

feedback inhibition

How Cells Control Product Buildup

Cells use enzymes to run biochemical reactions and make the products they need. These reactions are happening constantly, and enzymes speed them up so they happen fast enough to matter. Enzyme activity also has to be regulated. Cells need the right amounts of starting materials, intermediate metabolites, and final products. If these substances build up too much or drop too low, the cell can be harmed. That is why cells use control systems to keep metabolic levels balanced. One important...

allosteric regulation

Allosteric Control of Enzyme Speed

Allosteric control changes enzyme speed when a molecule binds to a site other than the active site. That alternate binding spot is called an allosteric site. An enzyme can have more than one allosteric site. This type of control can raise or lower enzyme activity. Many enzymes with allosteric control are metabolic enzymes. They help with the breakdown or the building of specific molecules in cells. In allosteric inhibition, the effector molecule causes a shape change that lowers the enzyme's...

cofactors and coenzymes

Enzyme Helpers: Metals, Vitamins, and More

Enzyme helpers are needed for many enzymes to work properly. These helpers fall into two groups: cofactors and coenzymes. Cofactors are metallic ions, while coenzymes are non-protein organic molecules. Both can be tightly bound to an enzyme or attach only when the substrate binds. Cofactors are common in mature proteins, appearing in about 30% of them. They are often added as the enzyme folds and help with catalytic activity. Magnesium is one important cofactor, and it is needed by more than...

key terms and concepts

Compare competitive and noncompetitive enzyme inhibitors, including active-site binding, allosteric effects, disulfiram, and how inhibitors regulate cells.

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Competitive vs Noncompetitive Inhibitors

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