Re: Why does adding an inhibitor of ATP synthase allow ADP to be > than ATP

We were a bit uncertain if this was a question from an asignment. As we 
are not supposed to do anyone's homework, I decided that I would either 
have to answer "around" the question - i.e. not really answering but in 
many words, or wait a bit. I chose the latter.

Adenosine tri-phosphate (ATP) is a sugar with a chain of phosphates in 
one end: Adenosine-P-P-P, if you like. The binding between two phosphates 
is rich in energy and this is the cells "money" for energy if you like. 
Most enzymes that need energy pick up ATP and cleave it to ADP + P, but 
some go one step further: they make AMP + PP (Pyrophosphate) and then 
also cleave PP into two P, for an extra boost.

In a cell ATP is used for all kinds of activities that use up energy. If 
the transformation of X into Y does not happen by itself (or is too 
slow), then this reaction can be coupled to cutting off one P from ATP, 
giving ADP and a free phosphate. See the ATP as an apted spring: the 
enzyme (E) that makes Y out of X picks up a compressed spring (ATP) to 
drive the reaction by triggering the spring (cutting off a phosphate to 
make ADP).

In a cell going about its normal life, there are just so many springs 
around, i.e. [ATP] + [ADP] is about constant. What the ATP synthase does 
is to use another source of energy (respiration, photosynthesis etc) 
to “compress the springs that have been triggered somewhere else”: 
putting back a phosphate on ADP to make ATP again. Basically, in a living 
cell you have a huge amount of processes that make ADP out of ATP (using 
energy) and then a bunch of processes that make ATP out of ADP (storing 
energy). Round and round it goes. Can you picture this?

By adding oligomycin you block one of the main enzymes that put the P 
back on ADP to produce ATP. You push the system off balance: you still 
have the same amount of processes using up the ATP, but you don’t cycle 
it back anymore. Out of the pool of ADP+ATP, there will be less and less 
ATP and more and more ADP, but remember: the size of the pool is 
unchanged. However, if you measure the amount of ADP, and then the amount 
of ATP, what will you see? ADP is going up and ATP is going down. None is 
created: it’s like pouring water between two glasses.

Hope this helps.
Kind regards,
Erik