True about isoenzymes is:

Isoenzymes are the multiple forms of the same enzyme in a single species that catalyze the same chemical reaction or reactions, but differ from each other structurally, electrophoretically and immunologically. Though the same chemical reaction is catalyzed, the different isoenzymes may catalyze the same reaction at different rates. Isoenzymes have different pH optimes, Km and V max values. Isoenzymes may differ in their amino acid sequence and their quaernary structures. The isoenzymes may have different propeies also for e.g. LDH-4 and LDH-5 are easily destroyed by heat, whereas LDH-1 and LDH-2 are not, if heated upto 60degC. (Heat resistant). Individual isoenzymes (isozymes) are distinguished and numbered on the basis of electrophoretic mobility, with the number 1 being assigned to that form having the highest mobility toward the anode, for e.g. LDH-1 has the highest mobility towards the anode and LDH-5 is the slowest. Isoenzymes have different tissue distributions. Therefore the pattern of isoenzymes found in the plasma may serve as a means of identifying the site of tissue damage. Example of the diagnostic use of isoenzymes are the study of Lactate Dehydrogenase and Creatine Kinase.