Determination of the Diffusion Coefficient of Myoglobin in Muscle Cells

Myoglobin (Mb) serves as an intracellular store for oxygen in red muscles, ensuring aerobic metabolic processes during temporary respiratory or circulatory deficits in oxygen supply. Myoglobin can also contribute to sarcoplasmic oxygen transport by loading oxygen near the capillaries, diffusing to sites where the PO2 is low and releasing the oxygen there. To what extent this myoglobin-facilitated oxygen diffusion enhances the overall oxygen transport rate primarily depends on the cellular myoglobin concentration and on the mobility of this protein within the muscle cell. Myoglobin concentrations can easily be determined but until recently no direct measurements of the diffusion coefficient (DMb) of myoglobin in intact mammalian skeletal muscle cells have been performed. In many theoretical studies dealing with facilitated oxygen diffusion, therefore, estimates of the DMbvalue representing results from self-diffusion measurements in highly concentrated myoglobin solutions have been applied instead.