Enzymes are biological catalysts which increase the rate of biochemical reactions without undergoing any change themselves. They bind with the substrate to form a enzyme substrate complex leding to the formation of product releasing free enzyme.
Enzymes have an optimum pH at which they show their maximum activity. Any change in the pH effects the enzyme and the enzymatic reaction. Most of the enzymes are functional at the neutral pH of 7 in the cell cytoplasm with a few exceptions. An acidic environment in the cell, changes the tertiary structure of the enzymes and the bonds of the enzymes are weakened. Thus, preventing the substrate binding to the active site of the enzyme and inhibiting catalysis. This is due to the change in the structure of the active site leading to the lack of electrostatic attraction between the enzyme and the substrate.