Question

Activity of enzymes is the highest at an optimum pH and decreases for higher and lower pH conditions. The reason for this effect is:

protonation and/or deprotonation of amino acid side chains

reduction of disulfide bonds

competitive inhibition of enzymes by protons

non-competitive inhibition by protons

thermal denaturation of enzymes

Answer 1

protonation and/or deprotonation of amino acid side chains.

The change in pH can affect the ionisation of side chains. Acidic amino acids have carboxyl side chain and basic amino acids have amine functional group at its side chain. So the altered pH (at low pH so many H+ ions and at high pH so many OH-) can interact with these carboxyl and amine functional group and alters the ionization of amino acids thus the ionic bonds that help the 3D shape of the protein get affected. The shape of proteins influence the function and thus the enzyme become non-functional.