RESUMO
1. The pattern of purine base uptake in culture epimastigotes of Trypanosoma cruzi can be predicted from cell growth rate and cell concentration, with the late log phase showing the greatest variability. 2. Uptake rates are unexpectedly low in the reproductive tissue amastigotes and high in the non-reproductive blood trypomastigotes. It is suggested that blood trypomastigotes metabolize and accumulate reserves of purine metabolites, whereas amastigotes depend on degradation of host cell RNA and nucleotides as purine sources. 3. All parasite forms salvage hypoxanthine and guanine in preference to adenine. Nifurtimox, dipyridamole and cytochalasin have no effect on uptake, whereas amphotericin B, allopurinol, xanthine and urate inhibit it. The alterations caused by urate are complex, apparently involving inhibition of the monooxypurine phosphoribosyltransferase and induction of permeation of purines into the cells.
Assuntos
Purinas/farmacocinética , Trypanosoma cruzi/metabolismo , Adenina/metabolismo , Animais , Membrana Celular/metabolismo , Guanina/metabolismo , Hipoxantinas/metabolismo , Pentosiltransferases/farmacocinéticaRESUMO
The uptake of adenine, guanine and hypoxanthine by Trypanosoma cruzi culture epimastigotes was studied over short time periods at 22 degrees C. The uptake process is concentrative, driven by the purine phosphoribosyltransferases and saturable at about 10 microM hypoxanthine and 1 microM adenine or guanine. Each purine base is apparently taken up by a separate route and the oxypurines are regulated in parallel. Adenine inhibits oxypurine uptake. When the material was incubated with guanine or hypoxanthine for more than 2 min, a decrease in the nucleotide/free base ratio was observed, indicating inhibition of the guanine and hypoxanthine phosphoribosyltransferases. The uptake rates during the ascending phase of uptake and of culture growth rates were of the order of 50 for hypoxanthine and 20 for guanine, relative to that of adenine. These rates were within the physiological range for cell growth in these cultures. During the phase of descending growth and decreased purine uptake activity rates, uptake was depressed to 20% of the rates required for the growth observed in the cultures. It is proposed that the decline in growth rate leads to an increase of the nucleotide pools in the cells which inhibit uptake. This depression may be a cause of the mitotic blockade which occurs during the stationary phase.
Assuntos
Purinas/metabolismo , Trypanosoma cruzi/metabolismo , Adenina/metabolismo , Animais , Meios de Cultura , Guanina/metabolismo , Hipoxantinas/metabolismo , Pentosiltransferases/metabolismoRESUMO
We have previously shown the presence of various purine salvage enzymes in Trypanosoma cruzi, including phosphoribosyltransferase, aminohydrolase, kinase, phosphorylase and hydrolase activities. We now report that a similar situation occurs in Leishmania mexicana amazonensis and Trypanosoma brucei brucei. In all three organisms we found higher levels of activity for the phosphoribosyltransferase enzymes than for the nucleoside kinases, suggesting a preference for the salvage of purine bases rather than nucleosides. Similarly, absence of inosine phosphorylase activity suggests that only one route for the salvage of hypoxanthine is available to the three organisms. The most striking difference was that whereas T. cruzi and T. brucei possessed adenosine aminohydrolase activity, this was not detected in L. mexicana; instead adenine aminohydrolase activity was found. The overall similarity, as judged by the distribution of enzyme activities, of purine salvage in these three members of the kinetoplastida suggest a broad spectrum of activity for any inhibitor acting in this area; the plethora of alternative salvage pathways, however, suggests that in no case would such inhibition be cidal.