Aminooxyacetate Stimulation of Glycolate Formation and Excretion by Chlamydomonas

Glycolate formation during photosynthesis is characteristic of organisms which fix CO2 via RuBP3 carboxylase/oxygenase, particularly when CO2 concentration in chloroplasts is limiting (25,31). An oxygenolytic cleavage of RuBP, catalyzed by the oxygenase activity, followed by hydrolysis of phosphoglycolate by phosphoglycolate phosphatase are considered to be the major, if not the only, reactions leading to glycolate formation in leaves (6,22,25). Spinach chloroplasts also contain low activities (3-6 itmol/h-mg Chl [19,20]) of an NADPH-dependent glyoxylate reductase (GR) capable of producing glycolate from glyoxylate.

Section: Resultsmentioning

confidence: 99%

Inhibition of Spinach Leaf NADPH(NADH)-Glyoxylate Reductase by Acetohydroxamate, Aminooxyacetate, and Glycidate

Kleczkowski

Randall²,

Blevins³

1987

“…The induction of the excretion by AOA has been proposed to be due to an accumulation of a small amount of glyoxylate through the inhibition of the aminotransferase, since glyoxylate is a very potent inhibitor against glycolate dehydrogenase with a Ki of 10 /M, less than one-tenth of the Km of the dehydrogenase for glycolate (15). AOA at 1 mm seldom influences photosynthesis (9,14), and inclusion of this inhibitor in the incubation medium for photosynthesizing E. gracilis gives us an opportunity to investigate the relationship between the PCR cycle and glycolate metabolism. Figure 1 A shows the effects of 1 mM AOA on the excretion of glycolate and on the photosynthetic accumulation of paramylon, the reserve polysaccharide in Euglena cells.…”

Section: Materials and Methods Organismmentioning

confidence: 99%

“…The (14). The Euglena cells collected as the pellet were immediately killed with 80% acetone, and Chl and paramylon were determined as previously described (12 (14) and green algae (9) to excrete glycolate produced photosynthetically. The induction of the excretion by AOA has been proposed to be due to an accumulation of a small amount of glyoxylate through the inhibition of the aminotransferase, since glyoxylate is a very potent inhibitor against glycolate dehydrogenase with a Ki of 10 /M, less than one-tenth of the Km of the dehydrogenase for glycolate (15).…”

Section: Materials and Methods Organismmentioning

confidence: 99%

Evidence of Reentrance of Glycolate Carbon into the Photosynthetic Carbon Reduction Cycle in Photosynthesizing Euglena gracilis Z

Yokota¹,

Asama²,

Kitaoka³

1990

Aminooxyacetate induced excretion of glycolate from airgrown cells of Euglena gracilis in both air and 1% CO2 atmospheres. The rate of the excretion reached 70% of the photosynthetic rate in the air on a carbon basis, and was 10% in 1% CO2. The compulsory loss of photosynthetically fixed carbon as glycolate at the high rate in air in the presence of aminooxyacetate caused a decrease of the rate of synthesis of paramylon, the reserve polysaccharide. Analyses of the steady levels of photosynthetic intermediates showed that a decrease of the 3-phosphoglycerate level was the cause of the slow rate of paramylon synthesis under these conditions. The photosynthetic CO2 fixation enzyme, Rubisco,2 inevitably fixes O2 in the presence of 02. The resulting phosphoglycolate is hydrolyzed in the chloroplast to glycolate, the substrate of photorespiration. The rate of glycolate synthesis reaches 25 to 50% ofthe rate ofCO2 fixation in air atmosphere in the organisms, where Rubisco is the primary C02-fixing enzyme in photosynthesis (2,5,7,20).Glycolate is metabolized via the glycolate pathway in C3 higher plants (8 function of the glycolate pathway in these experiments. However, since any metabolite accumulated in excess in the presence of the inhibitors or in the mutants can affect growth and photosynthesis through influencing nonspecified steps (3), it is difficult for these studies to reach firm conclusions on the metabolic and physiologic functions ofthe metabolism. Elimination of the secondary effects of accumulated metabolites must be essential to obtain evidence for the hypotheses.Euglena and algal cells excrete glycolate, unlike C3 plants, when its metabolism is inhibited. We have found that AOA induces the excretion of glycolate with a small accumulation of glycolate and glyoxylate in the cells of E. gracilis (13,14). Therefore, the metabolic study of the effects of AOA on photosynthesis in Euglena may lead to an understanding of the metabolic relationship between the glycolate pathway and the PCR cycle. This paper describes our results.

“…The mode of action of AOA in these experiments is to be determined. 0 In an accompanying publication, Tolbert and his colleagues (11) employing Chiamydomonas present data on 14C labeling of glycolate during '4C02 photosynthesis in the presence of AOA.…”

Section: Discussionmentioning

confidence: 99%

Glycolate Formation and Excretion by Chlorella pyrenoidosa and Netrium digitus

Krampitz¹,

Yarris²

1983

Glycolate is a well-known photosynthetic product of 02-evolving forms of photosynthetic life (2, 4) which is excreted by algae (12) and chloroplasts (10). Conditions which favor glycolate formation and excretion are: high 02 partial pressure, low CO2 tension, and high light intensity. Under these conditions, the oxygenase activity of ribulose-P2 carboxylase forms 3-P-glycerate and 2-P-glycolate (6). The latter is dephosphorylated by a specific phosphatase (9). CO2 and 02 are competitive substrates for this enzyme activity. Experiments with 1802 have demonstrated that it is incorporated into the carboxyl group of glycolate by the action of the carboxylaseoxygenase enzyme (1).The goal of the research reported herein was an attempt to find conditions whereby the photosynthetic formation and excretion of glycolate could be obtained in high yields by algae in an atmosphere of air enriched with a low partial pressure of CO2 rather than a high partial pressure of 02 as employed by many investigators. The glycolate thus obtained could be enzymically converted to H2 for an energy source as depicted in