The multiple forms of an enzyme, catalyzing the same reaction are iso-enzymes (or isozymes). They, however, differ in their physical and chemical properties which include the structure, electrophoretic and immunological properies, Km and Vmax values, pH optimum, relative susceptibility to inhibitors and degree of denaturation.

Eg - Isoenzymes of Lactate dehydrogenase (LDH) - LDH1, LDH2, LDH3, LDH4 and LDH5.