Origin of Acetate in Spinach Leaf Cell

Liedvogel, Bodo; Stumpf, P.K.

doi:10.1104/pp.69.4.897

Cited by 69 publications

(42 citation statements)

References 31 publications

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“…1. Electron micrographs of spinach leaf mitochondria have been published elsewhere [15]. Oxygen uptake of the fractions was in the range of 460nmol 0, x min-' x mg protein-' and, thus, in accordance with published values [16].…”

Section: Characterization Of the Isolated Mitochondriasupporting

confidence: 68%

On the biosynthesis of ubiquinones in plant mitochondria

1984

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Isolated mitochondria from potato tubers, spinach leaves, and daffodil petals form intermediates of the ubiqujnone biosynthetic pathway (prenylated 4-hydroxybenzoate, prenylated phenols, and quinoid compounds) from [l -lSC]isopentenyl diphosphate and endogcnous or exogenous 4-hydroxybenzoate. In contrast [2-'4C]mevalonate 5-diphosphate, the immediate precursor of isopentenyl diphosphate was not accepted as a substrate. These results suggest that plant mitochondria have their own prenyltransferase and prenylation system, similar to the plastid compartment which also starts by the use of isopentenyl diphosphate [see Kreuz, K. and Kleinig, H. (1984) Eur. J. BiocArm. 141,

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Section: Characterization Of the Isolated Mitochondriasupporting

confidence: 68%

On the biosynthesis of ubiquinones in plant mitochondria

1984

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“…As an alternative to the export of acetyl-CoA via citrate, free acetate export from mitochondria, after acetyl-CoA hydrolysis (Liedvogel and Stumpf, 1982), cannot be ruled out because direct acetate export would lead to the same conclusions on isotope dilution as made with the export of citrate. However, some in vitro biochemical data suggest a lack of cytosolic acetyl-CoA synthase (Ke et al, 2000).…”

Section: Source Of Cytosolic Acetyl-coamentioning

confidence: 99%

Probing in Vivo Metabolism by Stable Isotope Labeling of Storage Lipids and Proteins in Developing Brassica napusEmbryos

2002

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Developing embryos of Brassica napus accumulate both triacylglycerols and proteins as major storage reserves. To evaluate metabolic fluxes during embryo development, we have established conditions for stable isotope labeling of cultured embryos under steady-state conditions. Sucrose supplied via the endosperm is considered to be the main carbon and energy source for seed metabolism. However, in addition to 220 to 270 mm carbohydrates (sucrose, glucose, and fructose), analysis of endosperm liquid revealed up to 70 mm amino acids as well as 6 to 15 mm malic acid. Therefore, a labeling approach with multiple carbon sources is a precondition to quantitatively reflect fluxes of central carbon metabolism in developing embryos. Mid-cotyledon stage B. napus embryos were dissected from plants and cultured for 15 d on a complex liquid medium containing 13 C-labeled carbohydrates. The 13 C enrichment of fatty acids and amino acids (after hydrolysis of the seed proteins) was determined by gas chromatography/mass spectrometry. Analysis of 13 C isotope isomers of labeled fatty acids and plastid-derived amino acids indicated that direct glycolysis provides at least 90% of precursors of plastid acetyl-coenzyme A (CoA). Unlabeled amino acids, when added to the growth medium, did not reduce incorporation of 13 C label into plastid-formed fatty acids, but substantially diluted 13 C label in seed protein. Approximately 30% of carbon in seed protein was derived from exogenous amino acids and as a consequence, the use of amino acids as a carbon source may have significant influence on the total carbon and energy balance in seed metabolism. 13 C label in the terminal acetate units of C 20 and C 22 fatty acids that derive from cytosolic acetyl-CoA was also significantly diluted by unlabeled amino acids. We conclude that cytosolic acetyl-CoA has a more complex biogenetic origin than plastidic acetyl-CoA. Malic acid in the growth medium did not dilute 13 C label incorporation into fatty acids or proteins and can be ruled out as a source of carbon for the major storage components of B. napus embryos.Plant oils represent the largest renewable resource of highly reduced carbon chains and there is interest in increasing their production by oilseed crops. Brassica napus (canola, oilseed rape) is a major oil crop and a multitude of literature focuses on the biochemistry and physiology of oil accumulation in developing seeds of B. napus (see Singal et al., 1987;Murphy and Cummis, 1989;Kang and Rawsthorne, 1994;Eastmond and Rawsthorne, 1998;King et al., 1998). Although the biochemical pathways leading from Suc to oil storage are largely understood, a number of questions remain regarding, for example, the subcellular organization of reactions, and the origin of acetyl-CoA, reducing power, and ATP for fatty acid synthesis. These questions are particularly difficult to address using standard in vitro or organellar biochemical analyses that often result in loss of key activities. In addition, due to several reasons including dilution of isotopes by ...

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“…Several possible mechanisms for generating acetyl-CoA in the plastid for fatty acid biosynthesis have been described. However, the relative significance of each of these mechanisms is not yet clear (Mattoo and Modi, 1970;Elias and Givan, 1979;Liedvogel and Stumpf, 1982;Givan, 1983;Kaethner and ap Rees, 1985;Randall et al, 1989;Wurtele et al, 1998;Bao et al, 2000;Ke et al, 2000a). Recent studies indicate that the acetyl-CoA pool required for de novo fatty acid biosynthesis is primarily generated by the plastidic isoform of the pyruvate dehydrogenase complex (Ke et al, 2000a).…”

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Molecular Characterization of a Heteromeric ATP-Citrate Lyase That Generates Cytosolic Acetyl-Coenzyme A in Arabidopsis,

Fatland¹,

Ke²,

Anderson³

et al. 2002

Plant Physiology

194

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Acetyl-coenzyme A (CoA) is used in the cytosol of plant cells for the synthesis of a diverse set of phytochemicals including waxes, isoprenoids, stilbenes, and flavonoids. The source of cytosolic acetyl-CoA is unclear. We identified two Arabidopsis cDNAs that encode proteins similar to the amino and carboxy portions of human ATP-citrate lyase (ACL). Coexpression of these cDNAs in yeast (Saccharomyces cerevisiae) confers ACL activity, indicating that both the Arabidopsis genes are required for ACL activity. Arabidopsis ACL is a heteromeric enzyme composed of two distinct subunits, ACLA (45 kD) and ACLB (65 kD). The holoprotein has a molecular mass of 500 kD, which corresponds to a heterooctomer with an A 4 B 4 configuration. ACL activity and the ACLA and ACLB polypeptides are located in the cytosol, consistent with the lack of targeting peptides in the ACLA and ACLB sequences. In the Arabidopsis genome, three genes encode for the ACLA subunit (ACLA-1, At1g10670; ACLA-2, At1g60810; and ACLA-3, At1g09430), and two genes encode the ACLB subunit (ACLB-1, At3g06650 and ACLB-2, At5g49460). The ACLA and ACLB mRNAs accumulate in coordinated spatial and temporal patterns during plant development. This complex accumulation pattern is consistent with the predicted physiological needs for cytosolic acetyl-CoA, and is closely coordinated with the accumulation pattern of cytosolic acetyl-CoA carboxylase, an enzyme using cytosolic acetyl-CoA as a substrate. Taken together, these results indicate that ACL, encoded by the ACLA and ACLB genes of Arabidopsis, generates cytosolic acetyl-CoA. The heteromeric organization of this enzyme is common to green plants (including Chlorophyceae, Marchantimorpha, Bryopsida, Pinaceae, monocotyledons, and eudicots), species of fungi, Glaucophytes, Chlamydomonas, and prokaryotes. In contrast, all known animal ACL enzymes have a homomeric structure, indicating that a evolutionary fusion of the ACLA and ACLB genes probably occurred early in the evolutionary history of this kingdom.Acetyl-coenzyme A (CoA) is an intermediate metabolite that is juxtaposed between catabolic and anabolic processes. As the entry point for the tricarboxylic acid (TCA) cycle, acetyl-CoA can be considered the gateway in the oxidation of carbon derived from the catabolism of fatty acids, certain amino acids (e.g. Leu, Ile, Lys, and Trp), and carbohydrates. Furthermore, acetyl-CoA is the intermediate precursor for the biosynthesis of a wide variety of phytochemicals. Because membranes are impermeable to CoA derivatives, it can be inferred that acetyl-CoA is generated in at least four distinct metabolic pools representing the four subcellular compartments where acetyl-CoA metabolism occurs: plastids, mitochondria, peroxisomes, and the cytosol (Fig. 1). Therefore, plants should have distinct acetyl-CoA-generating systems in mitochondria (for the TCA cycle), in plastids (for de novo fatty acid biosynthesis), in peroxisomes (the product of ␤-oxidation of fatty acids), and in the cytosol (for the biosynthesis of isoprenoids, flavo...

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Origin of Acetate in Spinach Leaf Cell

Cited by 69 publications

References 31 publications

On the biosynthesis of ubiquinones in plant mitochondria

On the biosynthesis of ubiquinones in plant mitochondria

Probing in Vivo Metabolism by Stable Isotope Labeling of Storage Lipids and Proteins in Developing Brassica napusEmbryos

Molecular Characterization of a Heteromeric ATP-Citrate Lyase That Generates Cytosolic Acetyl-Coenzyme A in Arabidopsis,

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