How does ph affect enzyme controlled reactions

Every different type of enzyme has their own optimum pH value. This is the range of pH values that they'll work best in which means the chemical reactions that they catalyze for will be the fastest.

However, if the pH value in the environment is out of the optimum pH range, the enzyme may slowly slow down their reaction. This is due to the change of shape of the active site. When the pH gets too extreme, the enzyme may even be denatured. Which means their active site is completely changed and can no longer bind into substrates. They're no longer functional, and there's no way back.

Therefore, the pH can slow down or speed up the reactions which evolves enzymes, depending on the optimum pH value of that enzyme.