Some factors such as temperature, pH and change in substrate concentration or the binding of specific chemicals alter the tertiary structure of the protein; thereby affecting the activity of the enzymes.
Temperature and pH affect the enzyme activity. Low temperature inactivates the enzymes and high temperature denatures the enzymes. The enzyme activity increases steadily with an increase in pH and temperature up to the optimum pH and optimum temperature. Thereafter, with an increase in pH and temperature, enzyme activity decreases as they get denatured.
If the substrate concentration increases, initially the velocity of enzymatic reaction rises. In the final stage, the reaction reaches a maximum velocity or V max. This velocity does not rise any further even if there is an increase in substrate concentration. The reason is that at V max, there are no free enzyme molecules available that can bind with extra substrate molecules.
Binding certain chemicals to the enzyme, acts as a competitive inhibitor to the substrate. The molecular structure of the inhibitor closely resembles that of a substrate and it competes with the substrate for the substrate-binding site of the enzyme. As a result, the substrate cannot bind and enzyme action is reduced.