Question

How does pH affect proteins? Why do proteins have an optimum, minimum, and maximum pH at which they will function?

Answer 1

Answer :

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. Low pH would protonate the side chains of the amino acids while high pH would cause deprotonation of side chains. This change in ionization (protonation/deprotonation) alters the 3-D shape of the protein (Denaturation with the concommitant loss of its biological activity). This can lead to altered protein recognition or the protein might become inactive.

At optimum pH, proteins are maximally functional with right amount of ionization. Which gives right shape and solubility for the protein. In case of enzymes(which are proteins) the binding of the substrate to the catalytic site is greatly influenced by the pH.

Optimal pH would facilitate maximal binding of the substrate to the enzyme hence more products can be formed. A minimum pH is required to keep the ionization status of the active site, and a maximal pH at which enzymes still retain minimal function.