The ontogeny of creatine kinase isozymes

Abstract

The ontogeny of creatine kinase isozymes in the rat brain, heart, and skeletal muscle and the chicken skeletal muscle has been studied by agar gel electrophoresis and visualization of the enzyme by an optical test. In adult animals three creatine kinase isozymes are observed: isozyme I (brain) migrating toward the anode, isozyme III (skeletal muscle and heart) migrating toward the cathode, and isozyme II (heart) with an intermediate electrophoretic mobility. In the early stages of ontogeny only isozyme I is present in all organs investigated. In skeletal muscle isozyme I slowly disappears and is replaced first by isozyme II and finally by isozyme III. In the intermediary stages, mixtures of isozymes are present. The adult pattern is reached about 90 days after birth in the rat and at hatching in the chicken. In heart muscle a similar shift is observed as in skeletal muscle, but the changes start earlier and remain stationary at the (isozyme II + isozyme III) stage. In the brain isozyme I remains the only isozyme throughout life. The changes in the isozyme pattern in skeletal muscle during ontogeny are correlated with simultaneous morphological, biochemical, and physiological events. Possibly, active creatine kinase is a dimer. Two types of monomers (B or brain type and M or muscle type) may combine to form three species of active enzymes: BB, BM, and MM.