Transport of D-fructose and its analogues by Trypanosoma brucei.
Kinetic parameters for entry of D-fructose into Trypanosoma brucei brucei have been determined. The net uptake of D-fructose was found to be rapid and occurred at a rate which was comparable with that observed for uptake of D-glucose. The Km and Vmax were 3.91 +/- 1.58 mM and 69.1 +/- 7.2 nmol min-1 (mg protein)-1. D-Fructose was metabolized to pyruvate under aerobic conditions and to pyruvate and glycerol under anaerobic conditions in a manner similar to D-glucose. Comparisons of the kinetic parameters for D-fructose transport and metabolism indicated that uptake was rate limiting. Inhibition constants (Ki) for inhibition of 6-deoxy-D-glucose by D-fructose and D-fructose transport by 6-deoxy-D-glucose were consistent with the Km values for these two substrates. These interactions indicate that D-fructose and 6-deoxy-D-glucose share a single common transporter. 1,5-Anhydro-D-glucitol and 1,5 anhydro-D-mannitol (the fused pyranose ring analogues of D-glucose and D-mannose) have been found to interact well with the transporter, while L-sorbose (a D-fructose analogue with a pyranose ring) had only low affinity. However, 2,5-anhydro-D-mannitol (a fused furanose ring analogue of D-fructose) inhibited both 6-deoxy-D-glucose and D-fructose transport with a Ki of approx. 0.8 mM. The high affinity for 2,5-anhydro-D-mannitol (2-deoxy-D-fructofuranose) indicates that D-fructose is transported in the furanose ring form.(ABSTRACT TRUNCATED AT 250 WORDS)
Fry
A J
AJ
Department of Biochemistry, University of Bath, UK.
Towner
P
P
Holman
G D
GD
Eisenthal
R
R
D000818:Animals; D001693:Biological Transport, Active / Q000187:drug effects; D003847:Deoxyglucose / Q000031:analogs & derivatives / Q000493:pharmacokinetics / Q000494:pharmacology; D005632:Fructose / Q000031:analogs & derivatives / Q000378:metabolism / Q000493:pharmacokinetics*; D006860:Hydrogen Bonding; D007700:Kinetics; D015394:Molecular Structure; D009004:Monosaccharide Transport Proteins / Q000378:metabolism; D011773:Pyruvates / Q000378:metabolism; D019289:Pyruvic Acid; D014346:Trypanosoma brucei brucei / Q000378:metabolism*
D009004:Monosaccharide Transport Proteins; D011773:Pyruvates; D005632:Fructose; D019289:Pyruvic Acid; D003847:Deoxyglucose; C037904:6-deoxyglucose