Learn various factors that affect the activity of enzyme, such as, pH, temperature, substrate concentration, enzyme concentration, product concentration, presence of inhibitors or activators.

Enzyme activity is a measure of amount of products produced by enzyme per unit time. Different factors affect enzyme activity, such as pH, temperature, substrate concentration, enzyme concentration, product concentration, presence of activators or inhibitors.

Temperature : Increasing the temperature leads to an increase in the kinetic energy of enzymes and substrates in the system. This makes them more mobile and thereby increases the frequency of collisions between enzymes and substrates. A substrate has to collide favorably with its enzyme to get converted to product. Hence increasing the temperature generally increases the enzyme activity, until a particular temperature threshold value. The threshold temperature exists because the enzyme gets denatured as the temperature goes above this threshold value and thereby loses its ability to catalyze reactions. Hence there will be a specific temperature value or a specific range of temperature at which the enzyme exhibits maximum activity. Increasing or decreasing the temperature from this optimum temperature value leads to a decrease in enzyme activity.

pH : There are several ionizable groups in an enzyme. The protonation states of these ionizable groups changes as pH changes. Each ionizable group has a pKa value. The ionizable groups exist predominantly in protonated state when pH is below pKa and exist predominantly in deprotonated state when pH is above pKa. For an enzyme to be functional, some of these ionizable groups must be in their protonated state and some in deprotonated state. Hence, each enzyme will show maximum activity at particular pH or pH range at which all of its ionizable groups are in favorable protonated states. Increasing or decreasing the pH from this optimum pH value leads to a decrease in enzyme activity as some or all of these ionizable groups end up attaining unfavorable protonation states.

Substrate concentration : Enzyme activity initially increases as we increase the substrate concentration, as higher the number of substrates in the solution, greater the chance of a favorable collision between a substrate and its enzyme. Increasing the substrate concentration beyond a particular value will not lead to any further increase in enzyme activity as all the enzyme molecules will already be occupied by substrates and hence there will be no more enzyme molecules free to catalyze the additional substrate molecules. Hence, the enzyme activity initially increases as we increase the substrate concentration and then reaches a maximum activity point at a particular substrate concentration. Increasing the substrate concentration any further will not lead to any further increase in enzyme activity. Some enzymes also get subjected to substrate inhibition where high concentration of substrates inhibits the enzyme and thereby decreases its activity. In the case of such enzymes, increasing the substrate concentration beyond a particular point will actually lead to a decrease in enzyme activity.

Enzyme concentration : Increasing the enzyme concentration increases the enzyme activity as more substrates get converted to product in the presence of more enzymes. Once all the substrate molecules are bound by enzymes, increasing the enzyme concentration any further will not increase the enzyme activity.

Product concentration : An increase in product concentration will not increase the enzyme activity. In the case of many enzymes, an increase in product concentration generally inhibits the reaction and thereby leads to decrease in enzyme activity due to a phenomenon called product inhibition or feedback inhibition.

Activators are species that increase the activity of enzymes while inhibitors decrease the activity of enzymes.