Studies on the recycling of the transferrin receptor in Trypanosoma bruceiusing an inducible gene expression system

Uptake of host transferrin in bloodstream forms of Trypanosoma brucei is me diated by a heterodimeric, glycosylphosphatidylinositol-anchored receptor. After endocytosis, transferrin is delivered to lysosomes where it is proteo lytically degraded. Whether the heterodimeric transferrin receptor is retur ned to mediate several cycles in ligand uptake is undefined. By using an in ducible gene expression system we provide evidence for recycling of the tra nsferrin receptor in bloodstream forms of T. brucei. The metabolic half-lif e of the transferrin receptor in bloodstream-form trypanosomes is determine d to be 7 h which is comparable to the half-lives of recycling receptors in mammalian cells. The cycling time of the trypanosomal transferrin receptor is calculated to be 11 min. By means of the half-life and the cycling time , we calculated that each receptor is recycled 60 times before being degrad ed on average.