Human, rabbit, bovine, and porcine creatine kinase isoenzymes are glycoproteins

Human, rabbit, bovine, and porcine creatine kinase (CK) isoenzyme preparations were extensively purified by isoelectric focusing and high-performance liquid chromatography and tested for the presence of carbohydrate. In this study, all the CK isoenzymes demonstrated positive periodic acid-Schiff (PAS) reactions, indicating the presence of carbohydrate. It is concluded that CK is a glycoprotein as a carbohydrate, associated with the M subunit of human, rabbit, bovine, and porcine isoenzymes. Also, carbohydrate is an integral part of the B subunit of both rabbit brain and porcine heart CK. Loss of carbohydrate may be important in enzyme catabolism, yielding a pool of circulating modified CK protein that, to date, has remained undetected by traditional methods.