What are the Effects of Various Conditions on Enzyme Activity?

As the temperature rises, the rate of a chemical reaction in­creases owing to an increase in the number of activated molecules.

But when the temperature rises above a certain limit the enzymes looses its activity after destroying its tertiary structure. Similarly low temperatures, such as freezing temperatures, generally inactivate the enzyme.

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It, therefore, follows that for every enzyme under a given set of conditions there is a temperature at which the activity of en­zyme is at a maximum.

This is known as optimum temperature. For most animal’s enzymes, the optimum temperature lies between 40 to 50°C.

2. Effect of pH:

The hydrogen ion concentration or pH has a marked influence on the rate of enzymic reactions. Characteristi­cally, each enzyme has a pH value at which the rate is optimal, this is known as optimum pH.

The optimum pH is that pH at which a certain enzyme causes a reaction to progress most rapidly. On each side of this optimum pH the rate is lower and at certain pH’s an enzyme may be inactivated or even destroyed.

Therefore, in en­zyme studies, buffers are used to keep the enzyme at an optimum or at least a favourable hydrogen ion concentration.

The optimum pH is dependent on various conditions such as the kind of buffers, the

Particular substrate and the source of the enzyme may also have an influence shows the optimal pH value for some represen­tative enzymes.

The influence of pH on enzymic reactions may involve several different types of effect. Enzymes, like other proteins, are ampholytes and possess many ionic groups.

If the enzymic function depends on certain special groupings, these may have to be present in some instances in the un-ionized state and, in others, as ions. The ionic strength of the solution affects the velocity of enzyme reactions.

In some cases, the substrates are electrolytes, and the reaction may depend on a particular ionic or non-ionic form of the substrate.

Many enzymes are complex proteins having a non-protein part loosely bounded to the protein part.

Since both moieties are essential for activity, conditions that influence the conjugation will destroy the enzymic activity, although this dissociation is usually reversible, e.g. peroxidase is split into its two components which are inactive at acid pH values; readjustment of the pH solution to pH-7 restores the activity.

3. Concentration of enzyme:

Because the enzyme itself enters into the reaction by combining temporarily with the substraate the relative concentration of enzyme influences the velocity of the reaction.

4. Concentration of enzyme:

Because the enzyme itself enters into the reaction by combining temporarily with the substraate the relative concentration of enzyme influences the velocity of the reaction.

5. Concentration of enzyme:

Because the enzyme itself enters into the reaction by combining temporarily with the substraate the relative concentration of enzyme influences the velocity of the reaction.

This means that the velocity of an enzyme reaction is directly proportional to the concentration of the enzyme, provided that the substrate is present in excess and is, therefore, not rate limiting.

This is true at the, beginning of the reaction, but it may not hold true as the reaction continues, especially as the substrate is used up.

6. Concentration of substrate:

For a given quantity of enzyme, the velocity of the enzyme-catalyzed reaction increase as the concentration of substrate is increased, such a reaction is known as first order.

At first, this relationship is almost linear but if the concentration of substrate is increased to a great extent than the rate of the reaction may prove independent of the substrate concentration. Such a reaction is said to be in a zero order.

This means the enzyme becomes saturated with substrate or nearly so and further increase in substrate concentration has a negligible effect.

7. Other factors:

In general enzymes are inactivated in strong light. Ultraviolet light is especially effective in destroying enzyme activity.

X-rays may or may not destroy enzymes, depend­ing on the circumstances. The presence of salts may influence the enzyme activity by participating with the enzyme due to its protein nature.