Glyoxylate decarboxylation during photorespiration

Grodzinski, Bernard

doi:10.1007/bf00385004

Cited by 65 publications

(45 citation statements)

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“…Glyoxylate oxidation should yield 1 mol of CO2 (from the carboxyl carbon) and 1 mol ofa C1 fragment from the methylene carbon per mol of glycolate metabolized. Grodzinski (3) suggested that this C1 fragment may react with glycine to form serine or may be further oxidized to CO2. Depending on which reaction predominated, 50 to 100%1o of the carbon in glycolate metabolized by this pathway would be released as CO2.…”

Section: Discussionmentioning

confidence: 99%

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Mechanism of Decarboxylation of Glycine and Glycolate by Isolated Soybean Cells

Oliver¹

1979

Plant Physiol.

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Isolated soybean af _esophyll cells decarboxylated exogenously added Il-M4Clglycolate and 1l-'4CIglycine in the dark. The rate of CO2 release from glycine was inhibited over 90% by Isoicotinic acid hydrie ad about 80% by KCN, two ibitors of the glycine to serine p-us CO2 reaction. The release of CO2 from glycolate was inhibited by less tha 50% under the same conditon This indicates that about 50% of the CO2 released from glycolate occurred at a site other than the glycine to serine reaction. The SenSitivity of this alternative site of CO2 release to an hibitr of gycolate oxidase (methyl-2-hydroxy-3-butynoate) but not an inhibitor of the gluttegoxyate minotrnsferase (2,3-pxypoplonate) indicates that this alternative (isonicotinic acid hydrazide Insensitive) site ofCO2 rekase involved glyoxylate. Catalase inhibited this CO2 rease. Under the condtons used it is suggested that about half of the CO2 released from glycolate occurred at the conversion of glycine to serine plus CO2 whie the rag half of the CO2 lss resulted from the direct oxidation of glyoxylate by H202.The rate of glycine decarboxylatin by the glycine to serine reaction was renti controfled by the amount of NAD in the mitochondria. Mitochonral electron transport inhibitors, KCN and actinomycin A, inhibited glycine decarboxylation wbile an uncoupler, 2,4nditropenol, stimulted the reaction Competition within the mitochondria between the enzymes of dak respirtion ad glycine dearboxylation for imiting NAD may force sbstantial mnts ofthe glycolate formed to be decarboxylated by the direct oxidation of glyoxylate.In plant species where the primary photosynthetic carboxylation reaction involves the formation of P-glycerate catalyzed by ribulose bisP carboxylase, glycolate is synthesized in the light at rates which are approximately equal, on a molar basis, to the net rates of photosynthetic CO2 fixation (7,14, 16 Glycolate is usually assumed to be metabolized by the pathway outlined by Tolbert (13). In this reaction sequence (Fig. 1 resulting NADH is oxidized in mitochondrial preparations by the oxidative electron transport chain with the concurrent synthesis of 3 mol of ATP for each atom of oxygen taken up (1, 5). The serine thus formed is deaminated to hydroxypyruvate which is in turn converted to P-glycerate and then glycerate.In addition to being transaminated to glycine, glyoxylate may be further oxidized directly. H202 produced either from the glycolate oxidase reaction (2, 3, 15) or in the light by a Mehler reaction within the chloroplast (17) can be the oxidant (Fig. 1).Such a reaction may or may not be enzymic. The carboxyl carbon from glyoxylate is released as CO2. The C, fiagment from the acarbon forms formic acid from the reaction with H202. Grodzinski (3) has suggested that this C1 unit may supply a substrate for the hydroxymethyltransferase and react with glycine to form serine.The a-carbon could also be oxidized completely to CO2 and contribute to the photorespiratory CO2 loss.This

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Section: Discussionmentioning

confidence: 99%

“…H202 produced either from the glycolate oxidase reaction (2,3,15) or in the light by a Mehler reaction within the chloroplast (17) can be the oxidant (Fig. 1).…”

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confidence: 99%

Mechanism of Decarboxylation of Glycine and Glycolate by Isolated Soybean Cells

Oliver¹

1979

Plant Physiol.

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“…The photorespiratory CO2 can arise either from the direct decarboxylation of glyoxylate (9,19) or during the mitochondrial oxidation of glycine to NH3, C02, and methylene tetrahydrofolate by the enzyme glycine decarboxylase. In the latter case, NAD+ is the electron acceptor and it in turn is reoxidized by the mitochondrial electron transport chain (5,17).…”

Section: Methodsmentioning

confidence: 99%

Simultaneous Oxidation of Glycine and Malate by Pea Leaf Mitochondria

Walker¹,

Oliver²,

Sarojini³

1982

Plant Physiol.

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Mitochondria isolated from pea leaves (Pisum sativum L.) readily oxidized malate and glycine as substrates. The addition of glycine to mitochondria oxidizing malate in state 3 diminished the rate ofmalate oxidation.When glycine was added to mitochondria oxidizing malate in state 4, however, the rate of malate oxidation was either unaffected or stimulated. tricarboxylic acid cycle function.Several authors have suggested the total or partial inhibition of the tricarboxylic acid cycle in the light (1,2,7,10). Others have shown that the cycle continued in the light (3,8,15). The NADH produced by glycine oxidation can be used by malate dehydrogenase to reduce oxaloacetate to malate (17) and this malate can be linked by a shuttle system to the peroxisomal reduction of hydroxypyruvate to glycerate (12, 28).Isolated pea leaf mitochondria readily use both glycine and malate as substrates. In the experiments described, we added glycine to mitochondria metabolizing malate as a model reaction for determining the effect of photorespiratory glycine oxidation on tricarboxylic acid cycle function by these plants. MATERIALS AND METHODSDuring photosynthetic CO2 fixation by C-3 plants, a substantial amount of newly formed carbohydrate is oxidized back to CO2 by the process of photorespiration (29). The photorespiratory CO2 can arise either from the direct decarboxylation of glyoxylate (9, 19) or during the mitochondrial oxidation of glycine to NH3, C02, and methylene tetrahydrofolate by the enzyme glycine decarboxylase. In the latter case, NAD+ is the electron acceptor and it in turn is reoxidized by the mitochondrial electron transport chain (5, 17). Current data suggest that in soybean (20, 21) Mitochondria were isolated from 2-to 4-week-old greenhousegrown pea (Pisum sativum L.) seedlings. Younger plants could not be used because the high lipoxygenase activity precluded the isolation of well coupled mitochondria. After chilling for 1 h, the leaves and stems (approximately 300 g) were ground for 2 s in a 4-L Waring blender in 1 L of grinding medium (0.5 M sorbitol, 50 mM MOPS2-NaOH, pH 7.5, 5.0 mm EDTA, and 0.5% BSA). The inclusion of reducing agents, including 5 mm ascorbate, 2 mM DTT, 2 mm thioglycolate, or 10 mim cysteine, resulted in inconsistent coupling ratios and varying amounts of KCN-insensitive respiration and was avoided. The homogenate was filtered through two layers of Miracloth (Calbiochem) and the fitrate was centrifuged at 5,000g for 2 min.The mitochondria were then collected at 20,000g for 5 min. This pellet was resuspended in cold medium containing 0.5 M sorbitol, 20 mm MOPS-NaOH (pH 7.2), 0.1% BSA, and 2 mM glycine and centrifuged at l,000g for 10 min and then 7,000g for 10 min. The final pellet was resuspended in the same medium and either used directly or further purified on a Percoll (Pharmacia Fine Chemicals) gradient. In the latter case, 1 ml mitochondrial preparation was carefully layered atop a step gradient composed of (bottom to top) 2 ml each 40%1o, 25%, and 15% Percoll in 0.5 M sorbitol,...

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“…Glycolate formed in the Calvin cycle is converted to glyoxylate and then glycine, and two moles of glycine are converted to one mole each of serine, ammonia and C0 2 which is responsible for photorespiration and which comprises 25% of the carbon flowing through the glycolate pathway. The oxidation of glyoxylate forms one mole each of C0 2 and formate (6). However, its contribution to photorespiration has been considered to be small (8,17).…”

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confidence: 99%