Myoglobin, a mobile carrier of
oxygen, is without a doubt an important player central to the physiological function of heart and skeletal muscle. Recently, researchers have surmounted technical challenges to measure Mb diffusion in the living cell. Their observations have stimulated a discussion about the relative contribution made by Mb-facilitated diffusion to the total
oxygen flux. The calculation of the relative contribution, however, depends upon assumptions, the cell model and cell architecture, cell bioenergetics,
oxygen supply and demand. The analysis suggests that important differences can be observed whether steady-state or transient conditions are considered. This article reviews the current evidence underlying the evaluation of the biophysical parameters of
myoglobin-facilitated
oxygen diffusion in cells, specifically the intracellular concentration of
myoglobin, the intracellular diffusion coefficient of
myoglobin and the intracellular
myoglobin oxygen saturation. The review considers the role of
myoglobin in
oxygen transport in vertebrate heart and skeletal muscle, in the diving seal during
apnea as well as the role of the analogous
leghemoglobin of plants. The possible role of
myoglobin in intracellular
fatty acid transport is addressed. Finally, the recent measurements of
myoglobin diffusion inside muscle cells are discussed in terms of their implications for cytoarchitecture and microviscosity in these cells and the identification of intracellular impediments to the diffusion of
proteins inside cells. The recent experimental data then help to refine our understanding of Mb function and establish a basis for future investigation.