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I am familiar with adenosine diphosphate (ADP) and adenosine triphosphate (ATP), how one relates to the other, and how each is formed in cellular respiration and photosynthesis, but I am confused as to how regular adenosine is formed.

I was reading an article on caffeine which stated:

Caffeine is structurally similar to adenosine, a neuromodulator, whose formation is dependent on the relative rates of ATP breakdown and synthesis.

From this I concluded that ATP can be changed to regular adenosine, and adenosine back to ATP, but I cannot find anything else on the internet to support my conclusion. I was also wondering when and why your body would change ADP into adenosine instead of ATP. I assume that AMP plays a role in all of this, and possibly ADA.

I only have a high school level education in biology, so please bear with me. If you do not mind, please include a source in your answer so I can further research on my own. Thanks!

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    $\begingroup$ Adenosine monoposphate can be converted to adenosine by a 5’-nucleotidase. $\endgroup$ – canadianer Jun 6 '18 at 1:16
  • $\begingroup$ @canadianer that set me down the right track for the most part. I have one more question. Wikipedia says that ADP is converted to AMP like this: 2 ADP → ATP + AMP. What is the name of this process and where does it take place? $\endgroup$ – Cardinal - Reinstate Monica Jun 6 '18 at 1:30
  • $\begingroup$ @CardinalSystem that reaction is called adenylate kinase and takes place in almost every living cell. $\endgroup$ – Victor Chubukov Jun 6 '18 at 4:03
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    $\begingroup$ Perhaps someone could integrate these comments into a decent answer. Even the poster after he has finished his researches. I'd consider doing it myself but I know next to nothing about adenosine as neuro- signalling molecule, which seems to be the focus of this. $\endgroup$ – David Jun 6 '18 at 7:59
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For a full understanding I refer you to the KEGG pathway map which is fairly comprehensive in showing all the metabolic processes that CAN produce Adenosine. It's a bit daunting but if you find it on the map here it is interactive and you can see the enzymes and pathways involved. If you drill down it brings you to a host of papers and references in primary literature to back things up.

However the dominant process is as follows:

   2 ADP <=> ATP + AMP  

enacted by an adenylate kinase then:

   AMP + H2O <=> Adenosine + phosphate

enacted by adenosine 5'-monophosphate phosphohydrolase (a 5'-Nucleotidases )

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  • $\begingroup$ So the nucleotidase can reverse its own hydrolysis to produce AMP, and the adenylate kinase to produce ADP? $\endgroup$ – Cardinal - Reinstate Monica Jun 6 '18 at 18:00
  • $\begingroup$ The kinase is certainly reversible with almost an equal balance of each reaction. The nucleotidase I believe is but i don't have a watertight source on it yet. $\endgroup$ – Benedict Claxton Stevens Jun 7 '18 at 16:56

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