Creatine kinase: purification, characterization, and tissue distribution of the MM subtypes

The MM isozyme of creatine kinase can be separated into four subtypes by isoelectric focusing: MM3 (pI 6.90), MM2 (pI 6.70), MM1 (pI 6.45), and MMx (pI 6.25). Individual subtypes were produced and purified from canine heart and then separated by chromatofocusing. Subtypes could not be distinguished by relative molecular mass or kinetic properties. They differed slightly in amino acid composition. Canine and human necropsy tissues were studied to determine subtype distribution. Heart and skeletal muscle contained the most MM isozyme of creatine kinase and it was predominantly of the MM3 subtype.