Glycosome-associated tyrosine-phosphorylated protein in Trypanosoma brucei

Phosphorylation of protein at tyrosine residues is an important mechanism for regulating protein function in eukaryotic cells. In this report we have identified by immunoblotting the target for tyrosine phosphorylation in the protozoan parasite Trypanosoma brucei as a doublet band of protein with molecular masses of 200 and 220 kDa. Ultrastructurally, the tyrosine-phosphorylated protein was localized to the microbody-like organelles unique to kinetoplastid protozoa, called glycosomes. Inhibition of multiplication by the tyrosine kinase inhibitor genistein appeared to have very different kinetics in procyclic and blood-stream stage parasites. This is consistent with a glycosomal location for the target of tyrosine kinase as these life cycle stages differ substantially in their dependence on glycolysis which occurs in this organelle.