The effects of pH on enzyme-catalysed reaction include which of the following? A. The direction of the reaction may be influenced by the [H⁺]. B. The ionisation state of enzymes dissociating groups may be modified. C. The ionisation state of substrate may be modified. D. The protein may be denatured at certain pH values.

The pH of the medium will have its effect on a enzyme-catalysed reaction in one or the other form. The options B and C define the action of protons on the dissociating groups and substrate. Availability of H⁺ will enhance the ionising ability and therefore, will affect the direction of reaction. It is obvious for protein to get partially denatured during the process when pH fluctuates.