Salvage synthesis of purine nucleotides by Helicobacter pylori

Abstract

The incorporation of purine nucleotide precursors into Helicobacter pylori and the activities of enzymes involved in nucleotide salvage biosynthetic pathways were investigated by radioactive tracer analysis and nuclear magnetic resonance spectroscopy. The organism took up the nucleobases adenine, guanine and hypoxanthine, and the nucleosides adenosine, guanosine and deoxyadenosine. Any incorporation of deoxyguanosine by the cells was below the detection limits of the methods employed. The activities of adenine-, guanine- and hypoxanthine-phosphoribosyl transferases were established. The bacterium showed high levels of adenosine and guanosine nucleosidase activities and lesser activity for deoxyadenosine; no hydrolysis of deoxyguanosine was detected. Phosphorylase activities were not observed with any of the nucleosides. Phosphotransferase activities with similar rates were demonstrated for adenosine, guanosine and deoxyadenosine; and a weaker activity was detected for deoxyguanosine. No nucleoside kinase activities were observed with any of the nucleosides. The presence of adenylate kinase was established, but no guanylate kinase activity was observed. The study provided evidence for the presence in H. pylori of salvage pathways for the biosynthesis of purine nucleotides.

Helicobacter pylori Relies Primarily on the Purine Salvage Pathway for Purine Nucleotide Biosynthesis

“…11B). These results confirm the absence of adenosine kinase and guanosine kinase in H. pylori, as has been previously noted (1,16,50). Curiously, we found that the ⌬deoD mutant also was incapable of growth on the purine base adenine.…”

“…Purine salvage and utilization have previously been examined in H. pylori (18,49,50). Radiolabeling studies have been used to show uptake and incorporation of the purine bases adenine and guanine (and to a lesser extent, hypoxanthine) (50).…”

“…Radiolabeling studies have been used to show uptake and incorporation of the purine bases adenine and guanine (and to a lesser extent, hypoxanthine) (50). The presence of adenine, guanine, and hypoxanthine phosphoribosyltransferase activities have been measured from whole-cell lysates (50), and an in-depth look at the enzymatic nature of H. pylori's purified xanthine-guanine phosphoribosyltransferase demonstrated its ability to catalyze the formation of 6-oxopurines (18). One study has shown that H. pylori can grow in the absence of preformed purines as long as exogenous catalase is present (49).…”

Helicobacter pylori Salvages Purines from Extracellular Host Cell DNA Utilizing the Outer Membrane-Associated Nuclease NucT

“…This would allow H. pylori to surround itself with a perpetual nuclease cloud, which could aid not only in natural transformation, as has been previously shown (39,40), but also in the degradation of extracellular, host cell DNA. Once the DNA is broken down, purine bases can pass readily through the bacterium's porous outer membrane and subsequently be transported through the inner membrane by purine permeases, such as NupC, whose activity in H. pylori has been described previously in the literature (20,43).…”

“…Generally, it has been shown throughout the literature that the majority of laboratory/clinical strains of H. pylori grow best in vitro on the purine base adenine or hypoxanthine (14,15,(17)(18)(19)(20). Adenine is the most prominent purine in the blood (22), and of all the purine bases, it has been shown to be the most rapidly taken up and processed into nucleotides by H. pylori (43). All these findings, including the more recent discovery of adenosine deaminase activity in at least three H. pylori strains (16,17,20), have pointed to adenine/adenosine being the prominent purine base/nucleoside utilized by this bacterium.…”