THE CYANELLES (ORGANELLES OF A LOW EVOLUTIONARY SCALE) POSSESS A PHOSPHATE-TRANSLOCATOR AND A GLUCOSE-CARRIER IN CYANOPHORA-PARADOXA

Cyanelles from Cyanophora paradoxa can easily be isolated and assayed for their carrier composition by the silicone oil filtering technique. The present investigation demonstrates a P-i-translocator transferrin g phosphate, dihydroxyacetone phosphate and 3-phosphoglycerate in a co unter exchange mode in cyanelles as in chloroplasts of higher plants. The uptake of P-i is inhibited by dihydroxyacetone phosphate, phosphog lycerate and glucose-6-P, only poorly by phosphoenolpyruvate and not b y 2-phosphoglycerate. The inhibitors pyridoxalphosphate and 4,4'-diiso thiocyanostilbene-2,2' disulfonic acid at low concentration also affec t P-i-uptake. Cyanelles probably transport photosynthate (reductant an d ATP) by triosephosphates. This is the first demonstration of a phosp hate translocator in an organism of a low evolutionary scale. Cyanelle s also transport glucose which proceeds in two phases. In the lower co ncentration range (less than or equal to 2.5 mM), glucose penetrates b y facilitated diffusion, whereas transport follows first-order kinetic s at higher amounts (> 2.5 mM). In the low concentration range, glucos e-transport is affected by high concentrations of 3-O-methylglucose an d fructose. The physiological role of the glucose-transport carrier in Cyanophora is doubtful. It may function in transporting glucose into cyanelles if the carbon level inside them becomes limiting, e.g. in da rk periods.