The relative amount of an element within a living cell is usually significantly different from that in its surroundings. For example, the sodium concentration inside a cell is typically only 2% of that in the environment; on the other hand, the potassium concentration is much higher inside a living cell than outside of it. A similar relation is found with respect to magnesium and calcium: the magnesium level is higher in a cell, whereas the free calcium concentration inside is very low compared to that outside, especially as compared to seawater.
KeywordsATPase Activity Active Transport Sarcoplasmic Reticulum Aspartate Residue Proton Translocation
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