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Factors affecting enzyme activity

The activity of an enzyme can be affected by a change in the conditions which can alter the tertiary structureof the protein.

These factors affect enzyme activity: –

1. Temperature:

The optimum temperature for enzyme activity is 300C – 400C in animals and 200C – 300C in plants.

High temperature (above 450C) denatures enzymes due to degradation of linkages in its polypeptide chain whereas low temperature inactivates enzymes due to the reduction in speed of molecular movement.

Effect_of_temperature_on_enzymes activity
Effect of temperature
on enzymes activity

2. pH:

Most intracellular enzymes function near neutral pH with the exception of several digestive enzymes which work either in an acidic range of pH or alkaline.

effect of pH on enzyme activity
effect of ph on enzyme activity

3. Substrate concentration:

With the increase in substrate concentration, the velocity of the enzymatic reactionrises at first.

The reaction ultimately reaches a maximum velocity (Vmax) which is not exceeded by any further rise in the concentration of the substrate.
This is because the enzyme molecules are fewer than the substrate molecules and after saturationof these molecules, there are no free enzyme molecule to bind with the additional substrate molecule.

effect of substrate concentration on enzyme
effect of substrate concentration
on enzyme activity

Michaelis-Menten equation:

Leonor Michaelis and Maud Menten proposed a mathematical model in 1913, to determine the effect of substrate concentration in enzymatic reaction and they derived a relationship which is mathematically expressed as:
Km = Michaelis – Menten constant i.e., the substrate concentration to produce half maximum velocity.
V = The velocity of the reaction.
Vmax = maximum velocity.
[S] = substrate concentration.

Inhibition of enzyme action:

The activity of an enzyme is also sensitive to the presence of specific chemicals that bind to the enzyme.

When the binding of the chemical shuts of enzyme activity, the process is called inhibition and the chemical is called an inhibitor.

Types of inhibition:

1. Reversible inhibition: – It is temporary inhibition, and is overcome by increased concentration of substrate, dilution, and dialysis.

2. Irreversible inhibition: – This inhibition is of permanent nature, in which the inhibitor combines with a specific functional group of the enzyme through covalent bond.

It does not overcome by increased concentration of substrate, dilution or dialysis.

On the basis of competitiveness enzyme inhibition can be divided into the following types: –

(i) Competitive inhibition
(ii) Non-competitive inhibition
(iii)Allosteric inhibition

(i) Competitive inhibition: – This inhibition occurs due to substrate or increase enzyme analog.

In competitive inhibition, an inhibitor that resembles the normal substrate binds to the enzyme, usually at the active site, and prevents the substrate from binding to the active site.

During competitive inhibition, the inhibitor and substrate compete for the active site. The active site is a region on an enzyme where a particular substrate can bind.
In competitive inhibition, the inhibitor resembles the substrate, therefore, taking its place and binding to the active site of an enzyme. Increasing the substrate concentration would diminish the “competition” for the substrate to properly bind to the active site and allow a reaction to occur.

(ii) Non-competitive inhibition: – In this inhibition, inhibitor forms a complex with the enzyme at a site other than the active site.

(iii) Allosteric inhibition: – In this inhibition, Inhibitor binds to the enzyme at specific site other than active site and change the structure of the active site to affect substrate binding.

Allosteric modulation or feedback inhibition is an enzyme regulatory the mechanism where a product or intermediates of a reaction functions as a temporary allosteric inhibitor, (which combines with a regulatory site) if its concentration crosses the threshold value.

The end product inhibitor functions as negative modulator and the enzyme inactivated is called an allosteric enzyme.

Michaelis- Menten or Kmconstant is not applicable in allosteric enzymes.

Enzymes: Structure, Types, and Functions

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