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Their ''hypothesis'' was that whales and other aquatic animals can hold their breath for so long because they can store more oxygen in their muscles by increasing the concentration of myoglobin in each muscle cells. Specifically, they predicted that species could increase the concentration of myoglobin by increasing its solubility through increasing the net charge, so that there would be repulsion between the myoglobin protein even at high concentrations, which would prevent aggregation and precipitation. | Their ''hypothesis'' was that whales and other aquatic animals can hold their breath for so long because they can store more oxygen in their muscles by increasing the concentration of myoglobin in each muscle cells. Specifically, they predicted that species could increase the concentration of myoglobin by increasing its solubility through increasing the net charge, so that there would be repulsion between the myoglobin protein even at high concentrations, which would prevent aggregation and precipitation. | ||
Amazingly, they found an association between an animals' ability to hold its breath, high concentrations of myoglobin in muscle tissue, and a larger positive net charge of myoglobin. Typically, purified | Amazingly, they found an association between an animals' ability to hold its breath, high concentrations of myoglobin in muscle tissue, and a larger positive net charge of myoglobin. Typically, purified terrestrial mammal's myoglobin has a solubility of 20 mg/g in an aqueous solution at neutral pH ([[http://www.sigmaaldrich.com/content/dam/sigma-aldrich/docs/Sigma/Product_Information_Sheet/2/m0630pis.pdf Sigma Aldrich]]) which turns out to be the maximum level of myoglobin found in most terrestrial mammal's tissue. But whales and other aquatic mammals far exceed this solubility limit, e.g., whales have 70 mg/g. The way that they overcome the solubility constraint may be traced back to a modest increase in the net charge of myoglobin - from around +2 in terrestrial animals to around +4 in aquatic animals. | ||
<StructureSection load='1mbn' size='350' side='right' caption='myoglobin (PDB entry [[1mbn]])' scene='57/575026/Electrostatics/10'> | <StructureSection load='1mbn' size='350' side='right' caption='myoglobin (PDB entry [[1mbn]])' scene='57/575026/Electrostatics/10'> | ||
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However, a 3-fold increase in concentration of myoglobin ought to result in a similar fold increase in max time of breath holding, and the researchers show that body mass also makes a critical contribution to an animal's ability to hold its breath, with the overall equation for the contribution of body mass and myoglobin net charge as follows: | However, a 3-fold increase in concentration of myoglobin ought to result in a similar fold increase in max time of breath holding, and the researchers show that body mass also makes a critical contribution to an animal's ability to hold its breath, with the overall equation for the contribution of body mass and myoglobin net charge as follows: | ||
'''log (maximum time underwater) = 0.223*log(body mass) + 0.972*log(myoglobin net charge) + 0.891''' | |||
As Asian elephant's weight is ~3K Kg, and a sperm whale's weight is ~50K Kg, it is clear that the modest increase in net charge contributes about the same as the enormous difference in body mass to the maximum time underwater. | As Asian elephant's weight is ~3K Kg, and a sperm whale's weight is ~50K Kg, it is clear that the modest increase in net charge contributes about the same as the enormous difference in body mass to the maximum time underwater. | ||
=References:= | |||
{{Reflist}} | {{Reflist}} | ||