Different proton-sugar stoichiometries for the uptake of glucose analogues by Chlorella vulgaris. Evidence for sugar-dependent proton uptake without concomitant sugar uptake by the proton-sugar symport system.
The uptake of hexoses by Chlorella vulgaris is accompanied by the uptake of protons. For 6-deoxyglucose a stoichiometry of one proton taken up per sugar molecule has been measured, whereas for 1-deoxyglucose approximately two protons are taken up per sugar molecule. It was found that in the presence of 1-deoxyglucose a considerable proportion of "carrier" catalyzes the transport of protons without the concomitant transport of sugar. Presumably, the binding of sugar initiates the translocation of the carrier-proton-sugar complex, but whereas 1-deoxyglucose can still dissociate from the complex at the external side of the cytoplasmic membrane, the translocation of the carrier-proton complex continues. This conclusion was reached since (a) the composition of the translocated carrier-proton-sugar complex is the same for both sugar. Its formation is a first order reaction with respect to protons. (b) When 6-deoxyglucose, present inside cells, is exchanged for external sugar, the exchange ratio is two to one when the external sugar is 1-deoxyglucose, two molecules of 6-deoxyglucose are lost for each molecule of 1-deoxyglucose entering. This result indicates that during uptake of 1-deoxyglucose statistically only each second carrier molecule appearing at the internal side of the cytoplasmic membrane is carrying sugar.
D001665:Binding Sites; D001692:Biological Transport; D002708:Chlorella / Q000378:metabolism*; D003593:Cytoplasm / Q000378:metabolism; D003837:Deoxy Sugars / Q000378:metabolism*; D003847:Deoxyglucose / Q000378:metabolism*; D004734:Energy Metabolism; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008566:Membranes / Q000378:metabolism; D008757:Methylglucosides / Q000378:metabolism; D008954:Models, Biological
D003837:Deoxy Sugars; D008757:Methylglucosides; D003847:Deoxyglucose