Assimilation and metabolism of glucose by Dunaliella tertiolecta I. Uptake by whole cells and metabolism by cell free systems

Dunaliella tertiolecta, a green euryhaline flagellate, is unableto use glucose as a substitute for photosynthetically fixedCO₂ to maintain growth. Glucose, acetate, pyruvate, succinate,sucrose, glycerol, alanine and -ketoglutarate do not stimulateendogenous respiration in this alga. By incubating whole cellswith these compounds labelled with ¹⁴C, it was shown that onlyacetate, pyruvate and glycerol penetrated the cell at rateswhich might affect growth. These rates were still only of theorder of 10 m/(moles/hr/mg protein. Only acetate and pyruvatewere metabolized to CO₂ at appreciable rates, 20 and 80% ofthe total assimilated, respectively. Cell free preparations of D. tertiolecta metabolized glucoserapidly, up to 2 µmoles/hr/mg protein, with over 75% ofthe ¹⁴C-label being recovered as triose phosphate. Both thehexose monophosphate shunt and the Embden-Meyerhof pathway wereactive. When specifically labelled glucose was supplied, CO₂from the C-6 carbon was released more rapidly than from theC-6 position, in both whole cells and in the cell free extract. It is concluded that the failure of D. tertiolecta to use glucoseis due to membrane impermeability, not lack of hexokinase. Apossible basis for this impermeability is discussed in the lightof the metabolic sequence which seems to be active in this alga. ¹Colombo Plan Fellow, 1968–69. Present address: NaturalProducts Research Institute, Seoul National University, Seoul,Korea. ²Present address: Biology Dept. Queen's University, Kingston,Ont., Canada. (Received August 13, 1970; )