Effect of formycin A and protein inhibitors on adenosine transport in Trypanosoma vivax

Abstract

Formycin A (50 µM - 2.5 mM), a nucleoside analogue of adenosine, inhibited adenosine transport by 50%.  Some sulphydryl reagents have been identified as inhibitors of the transport mechanism.  For example, iodoacetate (5 mM) inhibited the transport process by 33% and 17% at 0.5 mM and 0.1 mM adenosine respectively.  In contrast, the transport of 1 µM adenosine was stimulated by 5 mM iodoacetate.  2.5 mM p-chloromercuribenzoate inhibited the same process by 15%, 29% and 33% at 1 µM, 0.1 mM and 0.5 mM concentrations of adenosine respectively.  2-Mercaptoethanol stimulated adenosine transport in all cases.   The differential effect of the different concentrations of these inhibitors at varied concentrations of adenosine confirms our earlier report that multiple modes of adenosine transport exists in Trypanosoma vivax.  Protection by 2-mercaptoethanol and inhibition by p-chloromercuribenzoate indicate the presence of a carrier system for the transport process.  Inhibition by iodoacetate shows that energy is required for transport.  Thus, facilitated diffusion and active transport processes are both implicated in the mechanism of uptake of adenosine into the cells.  these results also suggest that SH-groups are involved in the transport process because most of the reagents mentioned above are classical SH-group function effectors.  However, the nature of the involvement of SH-group in the transport process is not defined by the present results.