Acquisition of lipoproteins in the procyclic form of Trypanosoma brucei

The procyclic form of Trypanosoma brucei binds and internalizes bovine high density lipoprotein (HDL) particles in a saturable process; the binding an d uptake of I-125-labeled HDL are inhibited by excess unlabeled HDL. We cal culated that each procyclic trypanosome exposes approximate to 1.0 x 10(6) binding sites for bovine HDL, with an equilibrium dissociation constant (K- d) of approximate to 1.26 x 10(-7) M. Uptake of HDL particles does not occu r at 4 degrees C. At 28 degrees C, a significant amount of the internalized HDL particles were efficiently degraded through a process that is sensitiv e to the presence of 50 mu M chloroquine. These results suggested that the uptake of HDL particles in procyclic T. brucei may occur via receptor media ted endocytosis, leading to proteolytic degradation of the particles in an acidic and endocytic compartment. (C) 1999 Elsevier Science B.V. All rights reserved.