Studies on the sub-banding of creatine kinase MM and the "CK conversion factor"

In serum, the M subunit of creatine kinase (CK) isoenzymes, MM and MB, is modified by a heat labile factor. As a result of the modification three sub-bands of MM and two of MB can be demonstrated by agarose electrophoresis. Normal sera contain MM1 as the dominant sub-band with lesser amounts of MM2 and MM3. Following tissue damage the MM sub-band distribution changes as a result of the increased release of MM, which occurs as MM3. Immediately after coronary bypass surgery MM3 is the dominant sub-band to be replaced by MM2 and in turn by MM1. The factor responsible for the modification of the M subunit, the "CK conversion factor" has been partially purified and its molecular weight determined.