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Shaken and stirred: muscle structure and metabolism

Raul K. Suarez

Department of Ecology, Evolution and Marine Biology, University of California, Santa Barbara, California 93106-9610, USA

View larger version (65K): [in a new window]   Fig. 1. Cartoon of sarcoplasmic space showing actin and myosin filaments (white), and glycolytic enzymes (black) drawn to scale and at their approximate intracellular concentrations (redrawn and modified from Maughan and Wegner, 1989).

View larger version (14K): [in a new window]   Fig. 2. Diffusion coefficients, Dcyt, of globular proteins spanning a range of molecular mass (redrawn and modified from Arrio-Dupont et al., 2000). Included are data obtained using cultured myotubes microinjected with fluorescently labeled proteins (Arrio-Dupont et al., 2000) (filled circles) and data obtained by measurement of the rates of diffusion of enzymes out of skinned, adult fibers (open circles) (Maughan and Lord, 1988).

View larger version (8K): [in a new window]   Fig. 3. Hypothetical plot of substrate (S) and product (P and Q) concentrations as a function of distance, d, from two sequential pathway enzymes, E1 and E2. In this sequence, S is converted to P and then to Q, in reactions catalyzed by E1 and E2, respectively. Curves denoting changes in [S], [P] and [Q] as a function of d are purely hypothetical.

View larger version (17K): [in a new window]   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; CKMM, myofibrillar creatine kinase; CKcyto, cytoplasmic creatine kinase; CKmito, mitochondrial creatine kinase; ANT, adenine nucleotide translocase; ims., intermembrane space; ATPMM, ATP at the myofibrils; ATPcyt, cytoplasmic ATP; ATPim, ATP in the ims.; ATPm, ATP in the matrix space.