All the enzymes in your body work best at different pHs. For example, the protease made in your stomach works best at a pH of 2 which is why the hydrocloric acid in your stomach is the best condition for the enzymes.
But the protease made in your pancreas works best at pH 7 or 8.
Your body made a variety of different chemicals which help our enzymes work best.
In the stomach there are around 35 million glands in your lining secreting enzymes to digest proteins (protease). These enzymes work best in a acid pH, so your stomach also secretes a concentrated solution of hydrochloric acid from the same glands. Around 3 litres a day to be exact.