The Hexose‐Proton Symport System of Chlorella vulgaris

The specificity of the hexose transport system of Chlorella for sugars is the same as the specificity of sugar‐induced proton uptake. The K m ‐values of various sugars for the rate of proton uptake agree well with the respective K m ‐values for the rate of uptake of these sugars. Under anaerobic conditions in the dark, when the rate of sugar uptake is very low, sugar‐stimulated proton uptake is also hardly observable. Under the same conditions in the light [712 nm; O 2 evolution is inhibited by 3‐(3,4‐dichlorophenyl)‐1,1‐dimethylurea] sugar again stimulates proton uptake. The uncoupler carbonylcyanide‐ p ‐trifluoromethoxyphenylhydrazone, which inhibits sugar uptake, also prevents sugar induced proton uptake. The Stoichiometry for 6‐deoxyglucose and for glucose under various energetic conditions is one proton taken up per sugar molecule. For other glucose analogues the Stoichiometry has been found to be larger than one. Potassium and sodium ions cannot replace protons in the hexoseproton symport system.