Chicken heart muscle contains almost exclusively the BB isoenzyme of creatine kinase (CK), its myofibrils, moreover, lack an M-line. This tissue thus provides an interesting contrast to skeletal muscle, in which some of the MM-CK present as predominant CK isoenzyme is bound at the myofibrillar M-line. Approx. 2% of the total CK activity in a chicken heart homogenate remains bound to the myofibrillar fraction after repeated washing cycles; both the fraction and the absolute amount of CK bound are about threefold lower than in skeletal muscle. Almost all of the bound enzyme is located within the Z-line region of each sarcomere, as revealed by indirect fluorescent-antibody staining with antiserum against purified chicken BB-CK. After incubation with exogenous purified MM-CK, positive immunofluorescent staining for M-type CK at the H-region of heart myofibrils was observed, along with weaker fluorescence in the Z-line region. Chicken heart myofibrils may thus possess binding sites for both M and B forms of CK.
Localization of creatine kinase isoenzymes in myofibrils. II. Chicken heart muscle.
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T Wallimann, H J Kuhn, G Pelloni, D C Turner, H M Eppenberger; Localization of creatine kinase isoenzymes in myofibrils. II. Chicken heart muscle.. J Cell Biol 1 November 1977; 75 (2): 318–325. doi: https://doi.org/10.1083/jcb.75.2.318
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