Allosteric enzymes: mechanisms that can account for allosteric enzymes

its- asking- what-kinds- of- mechanisms- through- allosteric- and- proteins- - using- the- examples- and- the- advantages

Allosteric regulation is the regulation of activities of an enzyme or a protein caused by the binding of regulators at the site other than the active site of the enzyme or protein. Therefore, it causes the active site to change in shape and prevents the binding of the substrate. In that way, the activity of an enzyme is affected. The term "allosteric" comes from the Greek "allo" which means "other"; "steric" means "space." Example of allosteric regulations includes the feedback from downstream products, the feed forward from upstream substrates. An allosteric protein is a protein with multiple ligand-binding sites such that ligand binding at one site affects ligand binding at another, this is known as cooperative binding.

As we have known, an enzyme can convert itself between active and inactive conformations. In the present of regulator, for example, an inhibitor, fewer enzymes are available for free binding of substrates. However, as the inhibitor releases, the enzyme turns back to its original shape and the active site is available for substrate to bind and form product. The substrates form weak bonds with the active site and specificity of binding depends on the precise arrangement of atoms.

In the cell, the allosteric enzyme, which mostly have two or more subunits, can oscillate from active form to inactive form. Depends on which state of the enzyme, regulators can be used to stabilize the enzyme's conformation; the binding of an activator at regulator site can stabilize the active form of that allosteric enzyme while the binding of an inhibitor stabilizes the inactive form of the enzyme. The subunits of an allosteric enzyme fit together in a way that a conformational change in one subunit is transmitted to all others. through this interaction, a single activator or inhibitor molecule that binds to one regulatory site will affect the active sites of all subunits. In the cell, activators and inhibitors dissociate when at low concentrations which then allows the enzyme to oscillate again. This fluctuation of regulators can cause a sophisticated pattern of response in the activity of cellular enzymes. One example of this is the products of ATP hydrolysis which play a major role in balancing the flow of traffic between anabolic and catabolic pathways depending on their effects on key enzymes. For example, ATP binds to several catabolic enzymes allosterically which lowers their affinity for substrate and as a result inhibits their activity while ADP acts as an activator of the same enzyme. So if ATP production lags behind its use, ADP accumulates and activate these key enzymes that speed up catabolism, producing more ATP. If the supply exceeds demand however, catabolism slows down as ATP molecules accumulate and bind to enzymes, inhibiting them. In this way, allosteric enzymes control the rates of key reaction in metabolic pathways.

All enzymes must be tightly regulated to perform essential chemical reaction life.

Cooperativity

When the ennzyme can switch back and forth inactive and active form, the active form is not really stable and not always ready for substrates to bind. Copperativity involves the binding of one substrate to one active site (as the enzyme is in an active form)of one subunit triggers and "locks" all the other subunits in their active form in the way that the active form of the enzyme is stabilized, allowing more substrates to bind to other active site of other subunits.

To be more specific: Yes, you will have to include what you said: (effectors , modulators Rf orm and T from MM kinetics and sigmoid curves - remember that sigmoid curves are used instead of MM curves at allosteric enzymes)

You will also have to write examples of the advantages of allosteric regulation.
An obvious example is hemoglobin. As you know, hemoglobin is consisted by four polypeptide chains, and each chain can bind with on oxygen or CO2 molecule.
If one (or more) of the chains are binded to oxygen, then, an allosteric change will increase hemoglobin's affinity to oxygen.
Respectively, if one (or more chains) are binded with CO2 (and H+), then the hemoglobin's affinity to CO2 will increase, and the affinity to O2 will decrease.

The advantage of this example are:
When hemoglobin is found to an environment with high concentration of oxygen, then much more oxygen will bind to hemoglobin.
When hemoglobin is found to an enfironment with low oxygen and (relatively) high concentration of CO2, then much more O2 will be released, and much more CO2 will be binded (compared to the case of hemoglobin not being allosteric)

From stryer's biochemistry:

Generally,  allosteric regulation provides better regulation of enzyme reaction and protein's use.