Biosynthetic mechanism of glycolate in Chromalium 6. Glycolate formation and metabolism under low O_2

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Under low O_2 (0.05 mM O_2) ,there was no measurable excretion of glycolate or glycine by Chromatium cells, unlike the case of their incubation under high (0.7 mM) O_2. However, upon addition of non-radioactive glycolate and glycine to the suspension medium, there occurred a measurable incorporation of ^<14>CO_2 into these compounds, which were then excreted extracellularly; the total radioactivities measured were approximately 15% of the total CO_2 fixed photosynthetically. This phenomenon could be ascribed to the dilution of the intracellular pools by the compounds added. The results indicate that under low O_2 the glycolate molecules produced are metabolically further transformed in the bacterial cells. The incorporation of ^<14>CO_2 into the extracellular glycolate fraction was maximal at 0.3 mM glycolate in both high and low O_2. Presumably, glycolate formed in the bacterial cells under both the high and low O_2 is metabolized in a similar manner, although the excess glycolate and glycine molecules are rapidly excreted. During glycolate metabolism CO_2 was evolved from an isonicotinylhydrazide-sensitive reaction, suggesting that the pathway < glycolate → glycine → CO_2 > was similar in green plants. The results thus indicate that studies on glycolate and glycine metabolism in the anaerobic bacterium, Chromatium, provide a useful model system for elucidating the mechanism of photorespiration in green plants.
日本植物生理学会の論文