Putrescine uptake of Leishmania mexicana promastigotes is tightly regulated by polyamine intracellular concentrations. This uptake, markedly stimulated after parasite treatment with alpha-difluoromethylornithine (DFMO) for 48 to 72 hrs., was strongly repressed by exposure of Leishmania cultures to exogenous putrescine or its derivative 1,4-dimethylputrescine. In contrast, spermidine, spermine, diaminopropane and cadaverine were unable to decrease putrescine transport. Both, the uptake induction as well as its specific feedback repression by increased levels of endogenous putrescine requires protein synthesis since they were abolished after addition of cycloheximide for several hours. Our results seem to indicate that putrescine transporter is a stable and specific protein which can be reversibly inactivated by a relatively unstable repressor.
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