Isozymes (iso enzymes) catalyze the same reaction but at different rates. They differ from each other structurally (d/t difference in quaernary structure), electrophoretically (d/t different number of charged acidic or basic amino acids), physically ie in physical propeies such as heat resistance (d/t genetically determined differences in aminoacid sequence).They differ in pH optima, Km and Vmax values as well as in enzymatic classification numbers.Isoenzymes have different tissue distribution and may contain various combinations of different subunits of multimeric complex. Isoenzyme LDH-1 with four 'H' subunit predominates in cardiac tissue, since hea expresses the H subunit almost exclusively. CPK-1 is found in brain ischemia