Name: allosteric control of enzyme speed
Uploaded: 2025-10-23T11:48:33.000Z
Duration: 1 min 8 s
Channel: JoVE

- La regolazione
allosterica è la regolazione

di un enzima attraverso un sito diverso,

rispetto al sito attivo degli enzimi.

Quando una molecola si
lega in questa posizione

chiamato sito allosterico,

il legame può indurre un
cambiamento nella conformazione

o nella forma dell'enzima.

Tale azione può aumentare l'affinità

dei siti attivi degli
enzimi per il substrato,

incrementando l'attività degli enzimi.

Un processo noto come
attivazione allosterica.

In un grafico reattività per
concentrazione di substrato

l'attivazione allosterica
può essere rappresentata

come una curva positiva a S,

con un tempo di ritardo che
serve all'enzima per attivarsi.

Poi, a causa dell'incremento
repentino di siti attivi

un'alta concentrazione
di substrato può legarsi

e velocizzare rapidamente la reazione.

Al contrario, se l'effettore
si lega all'enzima

e causa un cambiamento nella conformazione

che determina un decremento
dell'affinità per il substrato,

il processo si definisce
inibizione allosterica.

In questo caso, la funzionalità
dell'enzima decresce

e si verifica un calo
della reattività chimica

rispetto allo stato di attivazione.

<ol><li>Cornish-Bowden, A. Comprensione delle interazioni allosteriche e cooperative negli enzimi. Il giornale FEBS. 281 (2), 621-6332 (2014).</li><li>Tsai, C.-J., Nussinov, R. Meccanismo allosterico emergente dell'attivazione dell'EGFR in contesti fisiologici e patologici. Giornale biofisico. 117 (1), 5-13 (2019).</li></ol>

regolazione allosterica

Allosteric Regulation

La regolazione allostica degli enzimi si verifica quando il legame di una molecola in una posizione diversa dal sito attivo provoca un cambiamento nell'attività enzimatica. Questo tipo di regolazione può essere positivo o negativo, aumentando o diminuendo l'attività dell'enzima. La maggior parte degli enzimi che mostrano l'allosteria sono enzimi metabolici coinvolti nella degradazione o nella sintesi di specifiche molecole cellulari.

Nell'inibizione allosterica, il legame di una molecola al sito allostrico provoca un cambiamento di forma che riduce l'affinità dell'enzima per il substrato. Spesso, l'inibitore allosterico è un prodotto dell'enzima o del percorso enzimatico, permettendo ai prodotti enzimatici di limitare la propria produzione. Questo è un tipo di inibizione del feedback, che impedisce la sovrapproduzione di prodotti. Come esempio classico, la isoleucina è un inibitore allostrico di un enzima importante nella sua sintesi.

Al contrario, un attivatore allosterico provoca un cambiamento conformazionale che aumenta l'affinità di un enzima per il substrato. L'attivazione aldica aumenta drasticamente il tasso di reazione, come rappresentato da una reazione di tasso-substrato a forma di S. Ad esempio, il legame del ligando extracellulare al recettore EGF transmembrana provoca un cambiamento conformazionale che comporta l'attivazione dell'attività della chinasi intracellulare. Se un enzima è composto da più sottounità, il legame di un attivatore allostrico a una singola sottounità può causare un aumento dell'affinità e il cambiamento di forma per tutte le sottounità affiliate.

Regolazione allosterica

La regolazione allosterica degli enzimi si verifica quando il legame di una molecola effettrice a un sito diverso dal sito attivo provoca un cambiamento nel ...

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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 ability to bind its substrate. Often, the inhibitor is a product of the enzyme or pathway, so the product helps stop more of itself from being made. This feedback inhibition prevents overproduction.

A classic example is isoleucine, which acts as an allosteric inhibitor of an enzyme needed for its own synthesis. Allosteric activation works in the opposite way. An activator changes the enzyme shape so it binds its substrate more strongly. This can greatly increase reaction rate, and it is shown by a hyperbolic curve on a graph of reaction rate versus substrate concentration.

A well-known example of allosteric activation is the EGF receptor. When an extracellular ligand binds to this transmembrane receptor, it changes shape and increases the receptor's intracellular kinase activity. In enzymes with multiple subunits, binding of one activator to a single subunit can also increase the affinity and shape of the other linked subunits.

Allosteric Control of Enzyme Speed

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Stored Energy in Motion and Bonds

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...

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ATP breakdown releases energy for cell work. Adenosine triphosphate, or ATP, can lose one or two phosphate groups when water is added. This hydrolysis reaction is exergonic, which means it releases energy that the cell can use. When one phosphate group is removed, ATP becomes ADP, or adenosine diphosphate. Inorganic phosphate is also released. ADP can then be hydrolyzed again to form AMP, or adenosine monophosphate, after a second phosphate group is removed. ATP has a clear structure. It is...

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Enzymes speed up many chemical reactions in cells. They are biological catalysts, so they increase reaction speed without being consumed or permanently changed. They do this by lowering the activation energy needed to turn reactants into products. Enzymes are proteins that usually work by binding to a substrate, which is the reactant molecule they act on. They show substrate specificity, meaning they bind only certain substrates. This specificity depends mainly on the shape and chemical...

enzyme kinetics

Substrate Effects on Enzyme Rates

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

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...

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 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...

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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

Learn how allosteric activators and inhibitors change enzyme shape, affect reaction rate, and control feedback in metabolic pathways.

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Allosteric Control of Enzyme Speed

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