Two factors that can greatly affect how an enzyme works are pH and temperature.
pH: changes in pH will alter an enzyme's shape and affect the enzyme's active site such that it may not conform to the substrate and thus fail to bind to it. Enzymes are active only within a narrow pH range usually between 5 and 9. Different enzymes work best at different pH values. The optimum pH for an enzyme depends on where it normally works. For example, enzymes found in the intestines have an optimum pH of 7.5 while those of the stomach have an optimum pH of about 2.
Temperature: the temperature range over which enzymes show activity is limited between the melting point ( 0°C ) and boiling point (100°C) of water. If a temperature is too low there is no noticeable reaction rate because the enzyme is working at a temperature far below its optimum. If the temperature is too high, well above 100°C then thermal deactivation and even denaturing of the enzyme can occur.