The role of gene duplication in the evolution of purine nucleotide salvage pathways

Abstract

(b) adenine deaminase, adenosine deaminase, and adenosine monophophate deaminase

acid (c) guanine reductase and inosine monophosphate dehydrogenase. These homologies support the idea that substrate specificity is the outcome of gene duplication, and that the purine nucleotide salvage pathways were assembled by a patchwork process that probably took place before the divergence of the three cell domains (Bacteria, Archaea, and Eucarya). Based on the ability of adenine PRTase to catalyze the condensation of PRPP with 4aminoimidazole5carboxamide (AICA), a simpler scheme of purine nucleotide biosynthesis is presented. This hypothetical route requires the prior evolution of PRPP biosynthesis. Since it has been argued that PRPP, nucleosides, and nucleotides are susceptible to hydrolysis, they are very unlikely prebiotic compounds. If this is the case, it implies that many purine salvage pathways appeared only after the evolution of phosphorylated sugar biosynthetic pathways made ribosides available.

Purine nucleotides are formed de novo by a widespread biochemical route that may be of monophyletic origin, or are synthesized freom preformed purine bases and nucleosides through different salvage pathways. Three monophyletic sets of purine salvage enzymes, each of which catalyzes mechanistically similar reactions, can be identified: (a) adenine, xanthine, hypoxanthine and guaninephosphoribosyltransferases, which are all homologous among themselves, as well as to nucleoside phosphorylases