PUTRESCINE ACTIVE UPTAKE SYSTEM IN THE TRYPANOSOMATID CRITHIDIA-FASCICULATA

Using the insect Trypanosomatid Crithidia fasciculata as a model paras ite of mammalian pathogenic flagellates, i.e. Leishmania and Trypanoso ma spp., we have studied the kinetic and regulatory characteristics of the polyamine uptake system, Putrescine transport was age-dependent w ith maximum expression values at the proliferative logarithmic phase. Putrescine transport in Crithidia fasciculata was energy-dependent and against a putrescine concentration gradient. The integrity of the mem brane sulfhydryl groups was absolutely required for optimum transport rates, The specificity of this mechanism was studied in the presence o f a series of different chain length aliphatic diamines, showing the h igh specificity for putrescine and the poor effect of this series at t he highest concentration analyzed as well as the higher polyamines spe rmidine and spermine. Finally, the well-known inhibitor of polyamine b iosynthesis, DFMO, led to an upward regulation of putrescine uptake co rrelating with the depletion of intracellular polyamine pool. In addit ion, the presence of high concentrations of putrescine in the culture medium produced a downward regulation of this system.