The Chemical Biology of Phosphorus
Chapter 5: Pyrophosphoryl and Adenosyl Transfers from Mg–ATP
Published:29 Oct 2020
Special Collection: 2020 ebook collectionSeries: Chemical Biology
The Chemical Biology of Phosphorus, The Royal Society of Chemistry, 2020, ch. 5, pp. 161-176.
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Two additional modes of enzyme-catalyzed ATP cleavage are used to drive coupled equilibria in more limited but still metabolically central cases. Pyrophosphoryl transferases direct attack of cosubstrate oxygen nucleophiles on the central Pbeta of ATP, with resultant release of free AMP and pyrophosphorylation of the incoming nucleophilic oxygen. Most notably 5-phosphoribose is converted to 5-phosphoribose-1-pyrophosphate (PRPP) to initiate both pyrimidine and purine nucleotide biosynthesis, the building blocks for both RNA and DNA biosynthesis, activating C1 of PRPP for C–N bond formation on the way to all four RNA building blocks. The even rarer adenosyl transfers arise in two enzyme active sites where the cosubstrate nucleophile is directed to cleave the C5′–O-PPP of ATP. The result is adenosylation of the nucleophile. In one case the thioether sulfur of methionine is trigonalized as the sulfonium cation in S-adenosylmethionine, the universal methyl donor in metabolism. In the second case the nucleophilic cobalt I central atom of vitamin B12 is adenosylated to generate adenosyl-B12 as the active coenzyme form. Both adenosyl-B12 and SAM convergently give rise to 5′-deoxyadenosyl radicals in enzyme active sites that mediate radical rearrangements.