Bacteria have a salvage pathway for the pyrimidine bases.
Phosphoribosyltransferases allow PRPP to be added to purine bases to generate nucleotides () and are required for a functional, purine salvage pathway. H. pylori has two known phosphoribosyltransferases, HP0735 and HP0572, currently believed to encode guanine-phosphoribosyltransferase (Gpt) and adenine-phosphoribosyltransferase (Apt), respectively (, ). We were successful in completely deleting the H. pylori apt gene, and interestingly, defined medium growth assays in RnP medium showed a reduced ability of this mutant to utilize guanine or guanosine (and to a lesser extent, xanthine) for growth, while only marginal growth abnormalities were seen when the mutant when grown on adenine (A). This indicates that in H. pylori strain G27, Apt uses guanine as its primary substrate and that the conversion of adenine directly to ATP via Apt potentially is not the major mechanism for ATP generation when H. pylori is grown on adenine. When a copy of apt was inserted into the rdxA locus of the Δapt mutant strain, the ability to grow on guanine was restored (B).
Salvage and Biosynthetic Pathways
Nucleotide Synthesis via Salvage Pathway
A second form of gout results from partial or complete deficiency of a purine salvage enzyme, hypoxanthine-guanine phosphoribosyltransferase (HGPRT). This enzyme catalyzes the following reactions:
Purine & Pyrimidine Synthesis (de-novo) | easybiologyclass
It is not yet clear why this deficiency accelerates purine synthesis. One model states that in the absence of these salvage pathways, GMP levels decline which, in turn, modulates the feedback inhibition of PRPP amidotransferase by this nucleotide. Alternatively, it has been proposed that decreased flux through this salvage pathway causes PRPP to accumulate and this, in turn, accelerates flux through PRPP amidotransferase by substrate level control.