REGULATIONS OF ENZYMES

for

M.Sc (Biotech) IInd Semester Students

by

Dr. Sameer S. Bhagyawant School of Studies in Biotechnology, Jiwaji University,

Gwalior

Regulation of enzyme activity is important to coordinate different metabolic processes.

Enzymes are regulated by:

Controlling their concentration 1. Control of synthesis (activation or repression) 2.Degradation

Controlling the availability of substrate 1. Production, degradation, compartmentation of substrate 2. Reversible binding of competitive inhibitors

Controlling the activity of the enzyme 1. Reversible binding of modulators/effectors 2. Reversible or irreversible covalent modification

Regulatory enzymes

These are the enzymes (2 large groups) whose activity can be changed in response to cell needs.

Allosteric enzymes

Enzymes regulated by reversible covalent modification (reversible phosphorylation, reversible acetylation and so on)

There are enzymes which have properties of both groups.

Allosteric enzymes contain two different sites: the active site for catalysis allosteric site for regulation

The sites are located in distinct places of enzyme molecule.

Molecules that affect activity of an allosteric enzyme bind to the allosteric site. These molecules are called allosteric effectors.

Allosteric enzymes

Kinetics of allosteric enzymes. Effects of allosteric effectors Cooperative effect in multimeric enzymes. In a case of allosteric enzyme, the dependence of the reaction

velocity against substrate concentration is S-shaped curve. Homotropic allosteric effectors (activators) are substrate

molecules. Heterotropic allosteric effectors are molecules different than

substrates.

Allosteric effectors Allosteric activators/ positive

effectors: result in increasing the reaction velocity and in increasing the affinity of an allosteric enzyme to its substrate.

Allosteric inhibitors/ negative effectors: result in decreasing the reaction velocity and in decreasing the affinity of an allosteric enzyme to its substrate

Feed-back inhibition

A sequence of enzymatic reaction with a particular goat is considered as a system/pathway of enzymes.

'

• Feed-back inhibition is a way of regulation

of enzymatic system activity exerted via initial enzymes of the system. Initial

enzymes usually are allosteric

Regulation of enzyme activity by reversible phosphorylation

Phosphoryl group is added by an enzyme (phosphotransferase /kinase) to OH-group of Ser/Thr in the regulatory site of an enzyme. The regulatory site and the AS are different in both the function and the location in enzyme molecule.

Phosphoryl group is removed from the regulatory site by another enzyme (phosphatase).

3-D structure of an enzyme and its active site is being changed in response to phosphorylation. Therefore the activity of an enzyme can increase or decrease.

Phosphorylation and dephosphorylation is swiched on/off in response to hormones (glucagon, epinephrine, insulin).

Storage of glycogen and fats as well as cell cycle is controlled by enzymes subjected to reversible phosphorylation.

Glycogen phosphorylase is regulated by

phosphorylation and binding of modulators

Digestive proteases are regulated through irreversible covalent modification