O 2 storage, is the main function of myoglobin, while the others deny it completely [8-12]. Both the "oxygen store" and "facilitated diffusion" mechanisms of myoglobin functioning can be effective only at high Mb concentrations and very low p O2 in the cell (less than 3 mm Hg). Respectively, the level of protein saturation by oxygen (S MbO2) observed in hard working muscles should be low. For significant contribution of the myoglobinfacilitated O 2 diffusion, high rates of myoglobin lateral diffusion (D Mb) and large gradients of MbO 2 concentration, corresponding to low intracellular S MbO2 under high muscle loads, are also needed [8,11]. But modern experimental methods estimate p O2 values in hard working heart to range from 15 to 25 mm Hg (rather than 0.5-3 mm Hg, as previously thought), and S MbO2 values defined by the NMR technique do not fall below 85%, amounting to 92% of the total pool of the protein (rather than 10-30%, as found previously) [9,10,13]. The D Mb values in intact skeletal muscles appeared also to be 5-10 times lower than those used in calculations of contribution of the myoglobin facilitated O 2 diffusion to supplying cells with oxygen [10]. So that, this contribution is only 1.5-4% at p O2 <13 mm Hg [14].
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