As we all know, this is not a direct measure of ATP availability, but we can use it on the assumption that it is relatively stable and reflects the extent of the ATP reserve. In the absence of an ATP source the ATP/energy ratio is the sum of the energy/ATP conversion ratios and so can be regarded as a measure of how much ATP is actually available. It also is inversely related to the efficiency of ATP metabolism, as the amount of ATP available (energy/ATP ratio) is related to the rate of ATP uptake.
The rate of ATP breakdown is the rate that enters the cell from the environment, in the form of water or glucose. As with ATP, this has two components: the first is the total amount of ATP that enters the cell, so if there is sufficient free energy to do so then this must exceed the capacity of the cell to utilize this. There may be a lower rate if there is a very poor source of free energy, and thus an excess of ATP available, and the second is the rate at which the energy for making ATP enters the cell.
So the first part of this equation is the rate of ATP breakdown, and the second is the rate at which ATP enters the cell. But it is also important to also factor in how well the ATP/energy ratio is maintained by the cell. One way to do this is to look at both the breakdown rate and the rate at which ATP enters and leaves the cell. The former is the breakdown rate (i.e. the rate at which ATP enters the cell) and the latter is the rate at which electrons are transferred from the electron transport chain (the flow of electrons between the oxygen-containing part of the ATP transport chain, the electron accepting ATP synthase, and the carbon-containing part of the ATP transport chain, the electron donating enzyme ATP hydrolysis) and this, of itself, is usually the rate at which the breakdown rate is maintained.
Thus the efficiency of ATP synthesis and ATP transport may be influenced greatly by the efficiency of the ATP transport chain from the donor to the acceptor. So one way to think about the ATP breakdown rate is to also think about the breakdown efficiency that exists in the cell (and so one way to use ATP to measure its rate of uptake and utilization is actually to think about the rate at which the cell can “free up” ATP). For most of the time the breakdown rate is very high but for short periods the efficiency drops, as a result of
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