How do O2 molecules from solution get into ATP?

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Discussion Overview

The discussion revolves around the mechanism of ATP hydrolysis in the presence of water labeled with an oxygen isotope (18O). Participants explore how oxygen from the water is incorporated into the products of ATP hydrolysis, particularly focusing on the fate of the oxygen atoms during the reaction process.

Discussion Character

  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • Some participants propose that the hydrolysis of ATP involves water (H218O), suggesting that the phosphate released during the reaction contains an 18O atom.
  • Others argue that the ADP molecule takes an H atom from the H218O, implying a transfer of hydrogen during the reaction.
  • A participant questions the role of water in hydrolysis, stating that water is not a catalyst, which leads to a discussion about the bond strength in ATP and the role of ATPase enzymes.
  • One participant mentions that the mechanism of ATP hydrolysis is complex and references a paper for further reading.
  • Another participant explains that the reaction is reversible and that the oxygen atoms in the phosphate are chemically equivalent, leading to uncertainty about which oxygen atom is expelled during the reverse reaction.

Areas of Agreement / Disagreement

Participants express differing views on the role of water in ATP hydrolysis and the fate of the oxygen atoms. There is no consensus on the exact mechanism or the implications of the isotope labeling.

Contextual Notes

Some assumptions about the reaction mechanism and the behavior of oxygen atoms in the context of enzyme interactions remain unresolved. The discussion reflects a range of interpretations regarding the hydrolysis process and the incorporation of isotopes.

Kuzon
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This was a practice exam Q:
ATP is added to the myosin ATPase domain in water labeled with an oxygen isotope. After 50% of the ATP has been hydrolyzed, the remaining ATP is isolated and found to contain 18O. Explain.

I get how H2O is used in order to regenerate ATP from the Pi and ADP, but on all the diagrams I've seen online I can't see where the oxygen from that H2O goes.
 
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Kuzon said:
This was a practice exam Q:
ATP is added to the myosin ATPase domain in water labeled with an oxygen isotope. After 50% of the ATP has been hydrolyzed, the remaining ATP is isolated and found to contain 18O. Explain.

I get how H2O is used in order to regenerate ATP from the Pi and ADP, but on all the diagrams I've seen online I can't see where the oxygen from that H2O goes.
I assume that the water is H218O (18O being the isotope of O with atomic mass 18). The water hydrolyses the ATP releasing a phosphate molecule. That phosphate will contain an 18O atom and the now ADP molecule takes an H atom from the H218O. There must be a free H.

AM
 
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Andrew Mason said:
I assume that the water is H218O (18O being the isotope of O with atomic mass 18). The water hydrolyses the ATP releasing a phosphate molecule. That phosphate will contain an 18O atom and the now ADP molecule takes an H atom from the H218O. There must be a free H.

AM
I don't really understand the explanation. How can water hydrolyse the ATP when hydrolysis is a reaction... It's not like water is a catalyst?
 
Kuzon said:
I don't really understand the explanation. How can water hydrolyse the ATP when hydrolysis is a reaction... It's not like water is a catalyst?
The bond strength between the outer phosphates in the ATP is weak because of the strain due to strong repulsion forces between them. That strain is enough so that the bonds can be broken by hydrogen bonding with water molecules. ATPase enzymes act as a catalyst. There is a great deal of energy released once the bonds are broken because of large the repulsive coulomb forces between these phosphates.

AM
 
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The actual mechanism by which ATP hydrolysis occurs is the subject of this paper, which you may find interesting.

AM
 
I'm sorry I saw this thread so late. I think that reference, part of vast, important and fascinating story or stories may be too complicated and specialised for the general question and principle here.

What is happening is this: O18 labelled water attacks the enzyme-bound ATP creating enzyme-bound ADP and enzyme-bound O18-labelled Pi. While bound to the enzyme, this reaction is reversible. If it were reversed exactly, then the same labelled oxygen atom that had been Incprporated would be expelled of course. But all four O atoms of Pi are chemically equivalent. The enzyme-bound phosphate ion can rotate while sitting in the enzyme, and so the oxygen atom expelled in the reverse reaction will often be not the same one as entered and thus the ATP is reconstituted containing O18.
 

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