Dark and photometabolism of sugars by a blue green alga: Tolypothrix tenuis.

The carbohydrate metabolism of the autotrophically grown blue-green alga, Tolypothrix tenuis, was studied. The alga respires glucose, fructose, galactose, and ribose. About 60% of the glucose consumed is converted by starved cells into a glucose polysaccharide. Glucose uptake and O(2) consumption are not inhibited by 0.01 m arsenite or by 0.005 m iodoacetamide. The distribution of (14)C in the polysaccharide glucose was established after feeding of glucose-1-(14)C, -2-(14)C, -6-(14)C, ribose-1-(14)C, and fructose-6-(14)C. Randomization of isotope between the 2 halves of the glucose from polysaccharide is limited when the experiments are carried out in the dark. After an extended incubation glucose-2-(14)C yields a glucose molecule with isotope labeled approximately equal in C-1, C-2 and C-3. When the labeled glucoses were fed at a light intensity of compensation point, and in the presence of carbon dioxide, a greater degree of randomization of isotope occurred. The enhanced randomization of isotope is thought to result from an additional supply of triose phosphates as a result of photosynthesis which creates an environment favorable to the reversal of the glycolytic reactions.To account for the labeling patterns and the resistance of respiration to the inhibitors, it is proposed that the oxidative pentose phosphate cycle is the major pathway of carbohydrate breakdown in this alga.