Open AccessSpecificity of glucose transport in Trypanosoma brucei
Author(s) -
SEYFANG Andreas,
DUSZENKO Michael
Publication year - 1991
Publication title -
european journal of biochemistry
Language(s) - English
Resource type - Journals
eISSN - 1432-1033
pISSN - 0014-2956
DOI - 10.1111/j.1432-1033.1991.tb16362.x
Subject(s) - phloretin , phlorizin , trypanosoma brucei , ouabain , glucose transporter , chemistry , cytochalasin b , non competitive inhibition , biochemistry , glucose uptake , atpase , membrane transport , oxidative phosphorylation , sodium , biology , enzyme , in vitro , membrane , endocrinology , insulin , organic chemistry , gene
Glucose transport in the bloodstream form of the protozoan parasite Trypanosoma brucei was characterized by enzymatically measuring the d ‐glucose uptake. Uptake kinetics showed a concentration‐dependent saturable process, typical for a carrier‐mediated transport system, with an apparent K m = 0.49 ± 0.14 mM and V max = 252 ± 43 nmol · min −1 · mg cell protein −1 (equal to 2.25 × 10 8 trypanosomes). The specificity of glucose transport was investigated by inhibitor studies. Glucose uptake was shown to be sodium independent; neither the Na + /K + ‐ATPase inhibitor ouabain (1 mM) nor the ionophor monensin (1 μM) inhibited uptake. Transport was also unaffected by the H + ‐ATPase inhibitor N,N′ ‐dicyclohexylcarbodiimide (DCCD; 20 μM) and the uncoupler carbonylcyanide‐4‐(trifluoromethoxy)phenylhydrazone (FCCP; 1 μM). However, highly significant inhibition was obtained with both phloretin (82% at 0.13 mM; K i = 64 μM) and cytochalasin B (77% at 0.3 mM; K i = 0.44 mM), and partial inhibition with phlorizin (14% at 0.5 mM; K i = 3.0 mM). In each case, inhibition was noncompetitive, partially reversible (45%) for phloretin and completely reversible for cytochalasin B and phlorizin. Measurement of the temperature‐dependent glucose uptake between 25°C and 37°C resulted in a temperature quotient of Q 10 = 1.97 ± 0.02 and an activation energy of E a = 52.12 ± 1.00 kJ/mol for glucose uptake. We conclude that glucose uptake in T. brucei bloodstream forms occurs via a facilitated diffusion system, clearly distinguished from the human erythrocyte‐type glucose transporter with about a 10‐fold higher affinity for glucose and about a 1000‐fold decreased sensitivity to the inhibitor cytochalasin B.