Dimer structure of three creatine kinases MM from porcine skeletal muscle

Three active fractions, FI, FII, and FIII, of porcine muscle creatine kinase MM isozyme, which had been isolated as single peaks by repeated isoelectric focusing (IEF), were subjected to reconstitution experiments to study their dimer structure. The specific activities of the three fractions were almost uninfluenced by a dissociation-reassociation procedure. Only one component was observed on IEF after reassociation of the subunits of FII. Three components were observed on IEF after reassociation of subunits of FI and FIII. These results show that FII, with isoelectric point (pI) 6.57, has a homodimeric structure (M2M2), consisting of two identical subunits. FI and FIII, with pI 6.74 and pI 6.34, respectively, have heterodimeric structures (M1M2 and M2M3, respectively), consisting of two nonidentical subunits.