Temperature and pH both effect the rates at which a reaction takes place, and there exists an optimum value for each. Most proteins, and therefore enzymes, are active only within a narrow pH range usually between 5 and 9. Several factors are influenced directly by the pH in which the reaction takes place. The curve reprecents the ionization of certain amino acid residue that must be in a specific ionization state for enzyme activity. The inflection point of the curve is called the pK of the reaction and can identify amino acid residues essential to enzymatic activity.
Temperature can effect an enzyme in two ways.
One is a direct influence on the reaction rate constant, and the other is in thermal denturization of the enzyme at elevated temperatures. If a temperature is too low, there can be no noticable reaction rate since the enzyme is operating at a temperature far below its optimum. If the temperature at which the enzyme is operating at is well above 100 o C, then thermal deactivization can occur. Thermal deactivization of enzymes limits their useful lifetime in processing environments. Therefore, it is important in many preocess design and manufacturing levels to have the correct temperature of reaction.