Question

Enzyme activity is pH dependent. (We tested tyrosinase activity at pH 6.5, the pH of the NaH2PO4 buffer used.) Explain why pH influences enzyme activity; Give detail about how specific amino acid side chains might be affected in their role in catalysis by pH.

Answer 1

The pH of a solution can have several effects of the structure and activity of enzymes.

For example, pH can have an effect of the state of ionization of acidic or basic amino acids. Acidic amino acids have carboxyl functional groups in their side chains. Basic amino acids have amine functional groups in their side chains. If the state of ionization of amino acids in a protein is altered then the ionic bonds that help to determine the 3-D shape of the protein can be altered. This can lead to altered protein recognition or an enzyme might become inactive.

Changes in pH may not only affect the shape of an enzyme but it may also change the shape or charge properties of the substrate so that either the substrate  cannot bind to the active site or it cannot undergo catalysis.