Excretion of Glycolate, Mesotartrate and Isocitrate Lactone by Synchronized Cultures of Ankistrodesmus braunii.
Fixation of (14)CO(2) by synchronized cultures of Ankistrodesmus braunii was highest for young growing cells, low for mature cells, and lowest for dividing cells. The amount of (14)C excreted during photosynthesis followed the same trend. Cells at the end of the growing phase, after 10 hours of a 16-hour light phase, excreted nearly 35% of the total (14)C fixed as one product, glycolate. Dividing cells from the dark phase, when tested in the light, excreted only 4% as much glycolate-(14)C as the young growing cells. Dividing cells also excreted as much mesotartrate as glycolate and also some isocitrate lactone and an unidentified acid. None of these excreted acids were found inside the cells in significant amounts. Methods for isolation and identification of the excreted acids are present. With (14)C-labeled algae, it was shown that the excretion of glycolate was light-dependent and inhibited by 1,1-dimethyl-3-(p-chlorophenyl) urea. The excretion of labeled mesotartrate, isocitrate lactone, and an unknown acid, but not glycolate, also occurred in the dark. The excreted mesotartrate was predominantly carboxyl-labeled even after long periods of (14)CO(2) fixation. Since glycolate is known to be uniformly labeled, glycolate could not be the precursor of the carboxyl-labeled mesotartrate. The reason for the specific excretion of glycolate, mesotartrate, and isocitrate lactone is not known, but the metabolism of all three acids by the algae may be limited and each can form dilactides or lactones by dehydration. In this context isocitrate lactone was excreted rather than the free acid.
Chang
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Department of Biochemistry, Michigan State University, East Lansing, Michigan 48823.
Tolbert
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