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ATP ase vs. ADP ase

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ATP ase vs. ADP ase

Postby kk » Thu Nov 20, 2008 2:38 pm

Dears,

a simple question: every enzyme with ATP ase activity accepts ADP as substrate as well? Or are these two things absolutely unrelated?
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Postby MisterATP » Thu Nov 20, 2008 5:40 pm

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.
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Postby MrMistery » Fri Nov 21, 2008 10:09 pm

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.
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Postby kk » Tue Nov 25, 2008 2:43 pm

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
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Postby MrMistery » Tue Nov 25, 2008 10:39 pm

no, I don't think so...
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Postby mith » Wed Nov 26, 2008 2:17 am

atp only works on atp, you'd have to find like adp-ase for the second part
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Postby MrMistery » Thu Nov 27, 2008 4:38 pm

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.
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Re: ATP ase vs. ADP ase

Postby kk » Sun Nov 30, 2008 7:13 pm

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!
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Postby Borisfen » Mon Feb 16, 2009 8:11 am

"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)
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Re: ATP ase vs. ADP ase

Postby bellyjelly » Tue Jul 12, 2011 7:20 am

ATPases are a class of enzymes that catalyze the decomposition of adenosine triphosphate (ATP) into adenosine diphosphate (ADP) and a free phosphate ion. This dephosphorylation reaction releases energy, which the enzyme (in most cases) harnesses to drive other chemical reactions that would not otherwise occur. This process is widely used in all known forms of life.
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