ATP ase vs. ADP ase

[kk]

Dears,

a simple question: every enzyme with ATP ase activity accepts ADP as substrate as well? Or are these two things absolutely unrelated?

[MisterATP]

Do you mean whether ATPase splits ADP? If so, I know that ATP isn't equal to ADP. In many cases ADP is an inhibitor.

[MrMistery]

Any enzyme that breaks down ATP into ADP and phosphate will be able (in vitro) to bind ADP and phosphate and run the reaction in reverse, synthesizing ATP. That's because an enzyme works both ways, it is just a catalyst. Of course, ATP hydrolysis is exothermic and the concentrations favor the forward reaction in vivo. However, in vitro, I would dare to say that you can make pretty much every ATPase run in reverse, synthesizing ATP in the process.

[kk]

I mean can these two reactions be catalyzed by the same enzyme, which we just refer to as ATPase:

ATP - > ADP + Pi

ADP - > AMP - Pi


In other words, which enyzme can utiliye the energy stored in the macroerg bond of ADP?

tx

[MrMistery]

no, I don't think so...

[mith]

atp only works on atp, you'd have to find like adp-ase for the second part

[MrMistery]

Oh one more thing. There are enzymes that can remove phosphate groups from nucleotides. The enzyme apyrase can catalyse all of the following three reactions:
ATP -> ADP +Pi
ATP-> AMP +Pi
AMP-> Adenine +Pi
The apyrases are still referred to as ATPases because of their ability to hydrolyze ATP, although they can hydrolyze other substrates as well. It is a general case - some enzymes can (albeit at a lower rate) accept other substrates than the one they are supposed to.
But in general, an ATPase breaks down ATP, and an ADPase breaks down ADP.

[kk]

OK... so I think we can not make a general statement, there are just too many exceptions. Eventually, this is biology... For a particular ATPase enzyme I guess it would be possible to say whether it can do both, but not for all in general. Thank you!

[Borisfen]

"I mean can these two reactions be catalyzed by the same enzyme, which we just refer to as ATPase:"

If I am not badly mistaken, enzymes that can do ATP hydrolysis (ATP ==> ADP + Pi) are usually poor catalysts for ADP hydrolysis.
But as noted above, under appropriate conditions they can synthesize ATP form ADP, so in this case ADP will be a substrate (like in ATP synthase, for instance)