Occurrence of Heterogenous Forms of the Subunits of Creatine Kinase in Various Muscle and Nonmuscle Tissues and Their Behaviour during Myogenesis

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Abstract
Purified homodimeric creatine kinases from chicken were subjected to 2-dimensional gel analysis under dissociating conditions. The subunits M-creatine kinase and B-creatine kinase were resolved into a basic and an acidic subspecies with similar mobilities in the sodium dodecyl sulfate dimension. The M-creatine kinase subspecies were found in myogenic cells, fast muscle and slow muscle, and the B-creatine kinase subspecies were present in heart, gizzard and brain. The creatine kinase subunits were identified in these tissues by immunoreplicas of 2-dimensional gels, immunoprecipitations or coelectrophoresis with purified creatine kinase and all gave the same results. In the course of myogenic development in vitro the subspecies were synthesized coordinately and no indication was found for a differential regulation of any of the subspecies of the creatine kinase subunits. No radioactive P was incorporated into either subspecies; phosphorylation was ruled out as the source of heterogeneity. Peptide mapping analysis of partial proteolytic digests did not reveal differences among the subspecies of the same subunit. Both chicken and rat creatine kinase displayed this heterogeneity. All subspecies were observed after translation of chicken RNA in a cell-free protein-synthesizing system. The heterogeneity may be explained by the existence of multiple but closely related genes for the creatine kinase subunits.