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I understand the constituent parts of adenosine (adenine and ribose) and that it can be broken down from ATP anabolically. Can adenosine also be formed catabolically? If so, what is the mechanism?

What's the mechanism for combining ribose and adenine in the cell?

A general explanation or citation would work. No need for someone to go out of their way to draw pictures. Thank you very much!

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  • $\begingroup$ en.wikipedia.org/wiki/Purine_metabolism?wprov=sfla1 $\endgroup$ – Gerhard Feb 21 '16 at 18:09
  • $\begingroup$ I saw this page, but it only refers to the degradation of AMP to adenosine. I was looking for its formation from adenine and ribose. Sorry, but am I missing something there on the page? I am starting to wonder whether adenosine does not biologically form at all via ribose and adenine. $\endgroup$ – Blaise Feb 21 '16 at 18:57
  • $\begingroup$ Where it says "Biosynthesis", i.e. the first half of the page. It goes all the way to IMP - for the last steps to AMP you'll have to click the respective link. $\endgroup$ – Gerhard Feb 21 '16 at 19:20
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Adenosine is synthesised from Inosine Monophosphate (IMP) as the nucleotide form (adenosine monophosphate). IMP does not accumulate in the cell but is rapidly converted to AMP and GMP. AMP, which differs from IMP only in the replacement of its 6-keto group by an amino is synthesized in a two-reaction pathway.


In 1948, John Buchanan obtained the first clues as to how nucleic acids and their components are synthesized by describing the synthesis of purine ribonucleotides.

Buchanan investigated how this process occurs de novo by feeding a variety of isotopically labelled compounds to pigeons and chemically determining the positions of the labelled atoms in their excreted uric acid (a purine).

enter image description here

The biosynthetic origins of purine ring atoms. Note that C4, C5, and N7 come from a single glycine molecule but each of the other atoms is derived from an independent precursor.

The actual pathway by which these precursors are incorporated into the purine ring, was elucidated in subsequent investigations performed largely by Buchanan and by G. Robert Greenberg. These investigations showed that the initially synthesized purine derivative is inosine monophosphate (IMP),

(Here I am not going to explain the biosynthesis of IMP but focus on the former)enter image description here

IMP is converted to AMP (or GMP) in separate two-reaction pathways:

  • In the first reaction, aspartate’s amino group is linked to IMP in a reaction driven by the hydrolysis of GTP to GDP + Pi to yield adenylosuccinate.

  • In the second reaction, adenylosuccinate lyase eliminates fumarate from adenylosuccinate to form AMP (adenosine monophosphate).

    enter image description here

It is important to note that free adenine (and guanine) can be reconverted to corresponding ribonucleotides through salvage pathways requiring the enzyme Adenine phosphoribosyltransferase (APRT) (mediates AMP formation)

References

Voet and Voet Biochemistry: Section 28-1. Synthesis of Purine Ribonucleotides

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