The activities of enzymes depend on the temperature, ionic conditions, and pH of the surroundings. Some enzymes work best at acidic pHs, while others work best in neutral environments. Digestive enzymes secreted in the acidic environment (low pH) of the stomach help break down proteins into smaller molecules. The main digestive enzyme in the stomach is pepsin, which works best at a pH of about 1.5. These enzymes would not work optimally at other pHs. Trypsin is another enzyme in the digestive system which breaks protein chains in the food into smaller parts. Trypsin works in the small intestine, which is not an acidic environment. Trypsin's optimum pH is about 8. Biochemical reactions are optimal at physiological temperatures. For example, most biochemical reactions work best at the normal body temperature of 98.6˚F (37˚C). Many enzymes lose function at lower and higher temperatures. At higher temperatures, an enzyme's shape deteriorates, and only when the temperature comes back to normal does the enzyme regain its shape and normal activity. Inhibitors regulate the function of enzymes. Inhibitors bind to the active sites of the enzymes inhibit the formation of an enzyme-substrate complex that eventually will reduce the efficiency of the enzyme and decrease the amount of the product formed.