In their mammalian host the parasites have a simple metabolism. They use several biochemical substrates of their host, but this poses a practical problem. Since the parasite is coated with a thick monotonous layer of glycoproteins, how can it absorb the necessary metabolites? At the base of the flagellum there is a small invagination ("flagellar pocket"). This site is accessible to macromolecules, but not to macrophages. Endocytosis can take place here. The receptors in this pocket are possibly also variable. This invagination, since it is the site of an important interaction with the host, may turn out a weak spot of the parasite which can be exploited therapeutically. Trypanosomes have no receptors for the uptake of albumin, but do have receptors for the uptake of LDL (Low Density Lipoprotein). LDL is essential for the parasite. Suramin binds LDL. This may explain the action of this medicament (interference with the normal LDL uptake in the flagellar pocket) and perhaps also explain the concentration of this molecule in the parasite via this receptor-mediated mechanism.
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Medicine Notes
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