Fig. 4. Creatine kinase fluxes in working hearts, as resolved by ³¹P-NMR spectroscopy (redrawn and modified from Joubert et al., 2002). The diagram shows metabolites and fluxes occurring in three compartments: ATP-consuming sites (myofibrils only shown for simplicity), cytosol and mitochondria. In the study of Joubert et al. (2002), unidirectional fluxes were detected at the myofibrils and mitochondria, while CK fluxes in both directions are detected in the cytosol. Myof., myofibrils; CK_MM, myofibrillar creatine kinase; CK_cyto, cytoplasmic creatine kinase; CK_mito, mitochondrial creatine kinase; ANT, adenine nucleotide translocase; ims., intermembrane space; ATP_MM, ATP at the myofibrils; ATP_cyt, cytoplasmic ATP; ATP_im, ATP in the ims.; ATP_m, ATP in the matrix space.