Free-Energy of Hydrolysis of ATP Equation

Many of the endergonic reactions in a cell are driven by being coupled to the
reaction in which ATP is hydrolyzed to ADP and P_{i}

ATP → ADP + P_{i}

for which ΔG^{'o} is -30.5 kJ/mol.

The amount of work that can be accomplished by ATP hydrolysis under cellular conditions
(the free energy change for ATP hydrolysis, ΔG_{p}), can be calculated with
this living equation. Let's explore the effects of the concentrations of ATP, ADP, and P_{i}
on ΔG_{p}. We read in Box 13-2 that in red blood cells, the relevant concentrations
are: ATP, 2.25 mM; ADP, 0.25 mM; and P_{i}, 1.65 mM. Substitute these values into
the equation below and calculate ΔG_{p}. Now, see what happens when a cell has used
up 90% of its ATP, converting it to ADP and P_{i}. What is ΔG_{p} now?
What if the cell had used 99% of its ATP? Would ATP still be useful as an energy source for
endergonic processes under these conditions? What would happen to ΔG_{p} if
[ATP] and [ADP] were held at the levels given above, but [P_{i}] became 10 higher?

If the reaction ATP → ADP + P_{i} were allowed to go to equilibrium within a
cell, what would ΔG_{p} be?

Créditos

Original material from **Lehninger Principles of Biochemistry**, 5^{a} edición, de **D. Nelson and M. Cox**; 2009. ISBN: 0-7167-7108-X.

Dr. José Antonio Encinar. (IBMC-UMH)