Properties of Three Creatine Kinases MM from Porcine Skeletal Muscle

Abstract

The properties of three fractions (F_I, F_II, and F_III) of porcine creatine kinase MM, which have been isolated by isoelectric focusing, were compared. Sugars were not detected in them. Their carboxyl-terminal sequences were identical and were determined to be -Thr-Lys by digestion with carboxypeptidases A and B. Immunodiffusion and competitive radioimmunoassay could not differentiate the three fractions from one another. Their amino-terminal sequences revealed that they had different primary structures. At residue 1, although all the three fractions had Pro, F_I and F_III had an additional amino acid, Ser. At residue 23, only F_I had Leu in addition to Ser, the amino acid common to the three fractions. These results indicate that differences among the three fractions of porcine creatine kinase MM are based on differences in the primary structures of the subunits in their dimer structures, and confirm the conclusion that F_II is a homodimer and F_I and F_III are heterodimers, which was reported in the preceding paper [Takasawa, T. & Shiokawa, H. (1983) J. Biochem. 93, 383-388].