Formation and metabolism of glycolate in the cyanobacterium Coccochloris peniocystis
1992
Norman, E.G. | Colman, B.
The formation and metabolism of glycolate in the cyanobacterium Coccochloris peniocystis was investigated and the activities of enzymes of glycolate metabolism assayed. Photosynthetic 14CO2 incorporation was O2 insensitive and no labelled glycolate could be detected in cells incubated at 2 and 21% O2. Under conditions of 100% O2 glycolate comprised less than 1% of the acid-stable products indicating ribulose 1,5 bisphosphate (RuBP) oxidation only occurs under conditions of extreme O2 stress. Metabolism of [1-14C]glycolate indicated that as much as 62% of 14C metabolized was released as 14CO2 in the dark. Metabolism of labelled glycolate, particularly incorporation of 14C into glycine, was inhibited by the amino-transferase inhibitor aminooxyacetate. Metabolism of [2-14C] glycine was not inhibited by the serine hydroxymethyltransferase inhibitor isonicotinic acid hydrazide and little or no labelled serine was detected as a result of 14C-glycolate metabolism. These findings indicate that a significant amount of metabolized glycolate is totally oxidized to CO2 via formate. The remainder is converted to glycine or metabolized via a glyoxylate cycle. The conversion of glycine to serine contributes little to glycolate metabolism and the absence of hydroxypyruvate reductase confirms that the glycolate pathway is incomplete in this cyanobacterium.
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