RESUMO
Leishmania mexicana mexicana promastigotes, axenic amastigotes, and amastigotes derived from Vero cells were examined for de novo purine synthesis and mechanisms of purine salvage. Both promastigotes and axenic amastigotes were incapable of de novo purine synthesis, as shown by the lack of [14C]formate and [14C]glycine incorporation into purine nucleotide pools. However, the ready incorporation of [14C]hypoxanthine, [14C]adenine, and [14C]guanine suggested that purine salvage pathways were operating. In addition, a significant percentage (greater than or equal to 60%) of the total label from these purine precursors was associated with adenylate nucleotides. Nucleotide pool levels of axenic amastigotes were consistently greater but the specific activities were less than those of promastigotes, suggesting a slower rate of purine metabolism in the axenic amastigote form. Similar results were obtained from amastigotes isolated from infected Vero cells.
Assuntos
Adenina/metabolismo , Guanina/metabolismo , Hipoxantinas/metabolismo , Leishmania/metabolismo , Nucleotídeos de Adenina/biossíntese , Animais , Linhagem Celular , Chlorocebus aethiops , Nucleotídeos de Guanina/biossíntese , Hipoxantina , Leishmania/crescimento & desenvolvimento , Nucleotídeos de Purina/biossínteseRESUMO
Promastigotes of Leishmania braziliensis panamensis absorbed the purines adenine, hypoxanthine, adenosine and inosine by a combination of diffusion and mediated components. When the uptake rates for these substrates were corrected for diffusion and compared, the purine bases adenine and hypoxanthine were transported at a significantly slower rate than the purine nucleosides adenosine and inosine. Competitive interactions among those purines tested confirmed the presence of mediated and diffusion components and suggested that three transport loci may be operating (Fig. 6). The first transport locus, designated Locus 1, transported inosine, Locus 2, the purine bases hypoxanthine and adenine and Locus 3, adenosine. In addition, adenine and hypoxanthine inhibited the uptake of one another competitively. A comparison of Ki values derived from double reciprocal plots of labelled hypoxanthine and adenine uptake in the presence of the unlabelled substrates as inhibitors suggested that adenine has a greater affinity for the transport locus.