Allosteric Enzyme

Allosteric enzymes are a group of biocatalysts with the same features as an enzyme but do not exhibit the same kinetic behavior. When they bind with an effector, these enzymes change their framework, changing the allosteric enzyme’s binding affinity at a ligand bonding binding site. The activity of an allosteric enzyme is subjective to the sight of its effector and the kinetics to the amount of the effector.

An allosteric enzyme plays an essential role in the basic biological process, such as regulating metabolism and cell signalling. These enzymes are among the regulatory enzymes which act as the rate-determining step for various pathways and can control the overall rate of a metabolic pathway.

Define allosteric enzyme

Allosteric enzyme definition: They are proteins in nature and are colloidal. They are specific in their actions and can alter the rate of reaction. Some of the enzymes have an additional site known as allosteric sites. These sites are unique places, and an allosteric enzyme has more than one allosteric site. The enzymes with allosteric sites are known as allosteric enzymes.

Monod and Jacob, two Nobel laureates, introduced the term allosteric to describe an enzyme side that is different from the active site and can still influence enzyme activity.

Properties of allosteric enzymes

Allosteric enzymes show some major properties, like:

• They have multiple allosteric sites.
• The molecules that bind to the allosteric site are modulators or effectors.
• Allosteric sites are binding sites that are unique from an enzyme active site for binding sites for substrates.
• The modulator or effectors can be positive or negative, which will regulate the enzyme activity. If the allosteric effector is positive, the enzyme activity increases and the allosteric site is known as the activator site. Whereas when the allosteric modulator is negative, the enzyme activity is inhibited, and the site is known as the inhibitor site.
• The enzyme activity gets altered when it binds to an allosteric site, known as Cooperative binding.
• Allosteric enzymes have an S-shaped curve for reaction rate Vs substrate concentration.
• The enzyme is heterotrophic when the modulator has a structure different from the substrate.
• When the regulatory enzyme of a substrate and the modulator are identical, it is known as homo-tropic.
• Some enzymes can have more than one modulator.
• Enzymes with multiple modulators have different binding sites for each.

How enzymes control cellular activities?

Enzymes are considered the keys that control cellular activities. A single cellular task is completed through interconnected reactions in the metabolic pathway. Each response must take place in order and be catalysed by a specific enzyme that acts upon its substrate only.

The product from the reaction will typically act as the substrate of the subsequent response. Therefore the abundance and the activity of the enzymes will influence the metabolic flux or the rate of the metabolites, which will affect the overall cellular activities.

The rate of the entire metabolic pathway is controlled by one chemical reaction of the pathway, which is called the rate-limiting reaction. It is also also known as the step to determine the rate.

Regulation of Allosteric Enzyme

Allosteric enzymes are inhibited by the compounds that are developed during the pathway of the function of enzymes. Such substances are known as effectors or modulators, and they can easily make allosteric enzyme activities to get altered as the conformation is changed. Some of the crucial modulators of allosteric enzymes in carbohydrate metabolism are Adenosine monophosphate (AMP), adenosine triphosphate (ATP) and adenosine diphosphate (ADP).

The function of the enzyme depends on its state. The activation state of an enzyme is referred to as R, where the enzyme is on, and its activity is turned up. The enzyme is off in the tense state or T, and its activity is turned down. One molecule can bind with the allosteric site and make the enzyme modify from the T to R state, whereas a different molecule may bind with the same enzyme and alter from the R to T state.

Conclusion

Allosteric enzymes are a group of proteins whose catalytic activities depend on the presence and abundance of the effector, and their reactions do not follow the typical Michaelis-Menten kinetics.