Use of magnetic particles in bioprocesses has many advantages. They can be easily separated from reaction medium and stabilized in a fluidized-bed reactor by applying a magnetic field. The use of magnetic particles so reduces capital and operation costs.As is known, enzymes are amphoteric molecules including many acidic and basic groups. The charges of these groups change with the pH of the reaction medium. These changes can affect the active zone of the enzyme. As a result, pH affects the enzyme activity, solubility, and stability. Immobilization of an enzyme on a carrier may change the microenvironment of the enzyme. The pH optimum value of immobilized enzyme may shift from that of the free one.