Regulation of Enzymes: enzyme induction and repression, allosteric enzymes regulation.

Introduction:

The regulation of enzyme reaction velocity is critical for the coordination of many metabolic processes.
Because many substrates have intracellular levels in the range of the Km, the rates of most enzymes are responsive to changes in substrate concentration.
As a result, an increase in substrate concentration causes an increase in reaction rate, which tends to return substrate concentration to normal.
Furthermore, when physiologic conditions change, some enzymes with specialized regulatory functions respond to allosteric effectors and/or covalent modification, or their rates of enzyme synthesis (or degradation) change.
In this lecture we are going to study following mechanisms,

Cells can also alter the speed of enzyme degradation or, more commonly, the rate of enzyme synthesis to control the amount of enzyme present.
The increase (induction) or decrease (repression) of enzyme synthesis changes the overall population of active sites.
Enzymes whose production is regulated are frequently ones that are only required during particular developmental stages or under particular physiological circumstances.

e.g. increased levels of insulin as a result of high blood glucose levels cause an increase in the synthesis of enzymes associated with glucose metabolism.

Enzymes that are constantly in use, on the other hand, are usually not regulated by changing the rate of enzyme synthesis.
Changes in enzyme levels as a result of protein synthesis induction or repression are slow (hours to days), compared to allosterically or covalently regulated changes in enzyme activity, which occur in seconds to minutes.

Allosteric enzymes have a binding site other than the active site for effector molecules.
The binding changes the catalytic properties of the enzyme because it changes its conformation.
Effector molecules can be inhibitors or activators.
A well-regulated biological system is present in all organisms.
Various regulatory mechanisms operate in the body to monitor and adapt to changes in the inside and outside environment.
Gene expression, cell division, hormone production, metabolism, and enzyme production are all regulated to ensure proper development and survival.
Enzymes are regulated by allostery, in which binding at one site affects the binding at subsequent sites.
Properties

Biological catalysts speed up reactions through their action on enzymes.
The active site of allosteric enzymes, as well as the substrate-binding site, have additional sites. C-subunit refers to the substrate-binding site, and R-subunit or regulatory subunit refers to the effector binding site.
Allosteric sites can occur at more than one position on an enzyme molecule
They can respond to multiple conditions, which impact how they react biologically.
An effector is a binding molecule, which can be both inhibitory and activating
By binding an effector molecule to an enzyme, the enzyme's conformation is altered.
Enzymes that are activated increase their activities, while enzymes that are inhibited decrease their activities after they are bound.
S-curves are typical instead of hyperbolic curves for velocity vs substrate concentration graphs for allosteric enzymes.

Effects of negative positive effectors on an allosteric enzyme.

A. Vmax is altered.

B. The substrate concentration that gives half-maximal velocity (K0.5) is altered.

Substrate molecules can also act as effectors here.
A major component of this process is the activation of enzymes, also known as cooperativity, i.e., oxygen binds to hemoglobin.

The substrate is not the same as the effector. Activators or inhibitors of the enzyme can be used, e.g., CO2 binding to hemoglobin.

The two types of allosteric regulation are inhibition and activation, based on the action of the regulator.
Allosteric inhibition -

If a protein complex of an enzyme is bound to an inhibitor, the enzyme's activity decreases due to conformational changes at all the active sites.

Activators bind to active sites and increase their function, which in turn increases substrate binding.