Dark assimilation of acetate-14C by Anabaena flos-aquae

Acetate is assimilated in both light and dark by the blue-green alga Anabaena flos-aquae. Light uptake has an apparent Km of 6.0 mM and a maximum velocity of 6.0 μmoles/g per hour while the dark uptake rate is lower and proportional to external acetate concentration between 5 and 100 mM.Only 2 to 7% of the acetate-1-14C taken up in the dark is oxidized to 14CO2, and 4 to 5 times as much 14CO2 is released from acetate-1-14C as from -2-14C. Fluoroacetate and α-hydroxypyridyl methane sulphonate inhibit the uptake and release of 14CO2 from acetate in the dark. Radioactivity from acetate-14C is incorporated in the dark mainly into lipids and two amino acids, glutamic acid and leucine. Small amounts of radioactivity are incorporated into a restricted number of organic and α-keto-acids, and triose and hexose phosphates. These results are interpreted as indicating a lack of oxidation of acetate in the dark by a tricarboxylic acid cycle.