Utilization and transport of glucose in Olea Europaea cell suspensions.
Cell suspensions of Olea europaea var. Galega Vulgar grown in batch culture with 0.5% (w/v) glucose were able to transport D-[(14)C]glucose according to Michaelis-Menten kinetics associated with a first-order kinetics. The monosaccharide carrier exhibited high affinity (K(m) approximately 50 micro M) and was able to transport D-glucose, D-fructose, D-galactose, D-xylose, 2-deoxy-D-glucose and 3-O-methyl-D-glucose, but not D-arabinose, D-mannitol or L-glucose. D-[(14)C]glucose uptake was associated with proton uptake, which also followed Michaelis-Menten kinetics. The transport of 3-O-methyl-D-glucose was accumulative (40-fold, at pH 5.0) and the protonophore carbonyl cyanide m-chlorophenylhydrazone strongly inhibited sugar accumulation. The results were consistent with the involvement of a monosaccharide: proton symporter with a stoichiometry of 1 : 1. When cells were grown with 3% (w/v) glucose, the uptake of D-[(14)C]glucose followed first-order kinetics and monosaccharide:proton symporter activity was not detected. The value obtained for the permeability coefficient of hexoses in O. europaea cells supported the hypothesis that the first-order kinetics observed in 0.5% and 3% sugar-grown cells was produced exclusively by passive diffusion of the sugar. The results indicate that in O. europaea cells sugar levels have a regulatory effect on sugar transport, because the activity for monosaccharide transport was repressed by high sugar concentrations.
Oliveira
Jorge
J
Centro de Ciências do Ambiente, Department of Biology, University of Minho, 4710-057 Braga, Portugal.
Tavares
Rui M
RM
Gerós
Hernâni
H
D019325:3-O-Methylglucose / Q000378:metabolism; D001692:Biological Transport / Q000187:drug effects / Q000502:physiology; D002250:Carbon Radioisotopes / Q000378:metabolism; D002478:Cells, Cultured; D003847:Deoxyglucose / Q000378:metabolism; D005632:Fructose / Q000378:metabolism; D005690:Galactose / Q000378:metabolism; D005947:Glucose / Q000378:metabolism* / Q000494:pharmacology; D007700:Kinetics; D008353:Mannitol / Q000494:pharmacology; D031658:Olea / Q000166:cytology / Q000378:metabolism*; D027981:Symporters / Q000378:metabolism; D014994:Xylose / Q000378:metabolism
D002250:Carbon Radioisotopes; D027981:Symporters; D019325:3-O-Methylglucose; D005632:Fructose; D008353:Mannitol; D003847:Deoxyglucose; D014994:Xylose; D005947:Glucose; D005690:Galactose