| Utilization and Transport of Glucose in Olea Europaea Cell Suspensions (2002) | |||||||||||||
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| Cell suspensions of Olea europaea var. Galega Vulgar grown in batch culture with 0.5% (w/v) glucose were able to transport d-[14C]glucose according to Michaelis–Menten kinetics associated with a first-order kinetics. The monosaccharide carrier exhibited high affinity (Km ≈50 µM) 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-[14C]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-[14C]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. | |||||||||||||
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