  Active ion transport is very critical for living cells to maintain and
regular internal and external environment. It is known that adenosine
5'-triphosphate (ATP) is a general energy source that applies bond energy for
pumps to overcome ion concentration gradient. In this study, we introduce a
novel thermodynamic model for active ion transport, which allows the pump to
act as a 'Maxwell's demon', and also conforms to the second law of
thermodynamics. Transport against the gradient is caused by the thermodynamic
fluctuation with information recording in ATP stream. Besides, exhaustive
experiments about Na-K ATPase performed in the red cell ghost system are
reviewed to verify this model, and all the results can support the solvable
theory about the working mechanism of demon pumps. Our findings indicate the
possible role of ATP as an information carrier but not energy currency. The
high-energy phosphate bonds can improve the efficiency of information recording
in relevance to ion transport and may mainly convert to heat.
