The hexose uptake system of Chlorella: Is it a proton symport or a hydroxyl ion antiport system?

Publisher Website
Google Scholar
Abstract
2‐Amino‐2‐deoxyglucose is taken up by the hexose transport system of Chlorella. The uptake of the neutral sugar proceeds together with stoichiometric alkalization of the medium. The uptake of the positively charged sugar (i.e., with a protonated amino group) proceeds as uniport and is not accompanied by net proton uptake but by charge compensating exit of proton and potassium. Thus the proton at the amino group replaces the cotransported ion, which therefore has to be a proton and not a hydroxyl ion. A depolarization of the membrane from − 130 mV to − 70 mV increased the K m‐value 3‐fold without change of V max. It is concluded that neutral sugar and proton are bound in close vicinity at a site in the middle of the membrane and that transport of sugar and proton occurs simultaneously.