Two d-2-Hydroxy-acid Dehydrogenases in Arabidopsis thaliana with Catalytic Capacities to Participate in the Last Reactions of the Methylglyoxal and β-Oxidation Pathways

Abstract

L-and D-lactate dehydrogenases belong to evolutionarily unrelated enzyme families (1). L-Lactate is oxidized by L-lactate: NAD oxidoreductase (EC 1.1.1.27), which catalyzes the reaction L-lactate ϩ NAD 3 pyruvate ϩ NADH, and by L-lactate cytochrome c oxidoreductase (L-lactate cytochrome c oxidoreductase, EC 1.1.2.3), which catalyzes the reaction L-lactate ϩ 2 cytochrome c (oxidized) 3 pyruvate ϩ 2 cytochrome c (reduced). Both groups are found in eubacteria, archebacteria, and eukaryotes. All known plant sequences belong to the EC 1.1. Although L-lactate dehydrogenase belongs to the most intensely studied enzyme families (2, 3), our knowledge about the structure, kinetics, and biological function of D-LDH 3 is limited. D-LDHs have mainly been identified in prokaryotes and fungi where they play an important role in anaerobic energy metabolism (4 -10). In Saccharomyces cerevisiae and Kluyveromyces lactis, a mitochondrial flavoprotein D-lactate ferricytochrome c oxidoreductase (D-lactate cytochrome c oxidoreductase), catalyzing the oxidation of D-lactate to pyruvate, is required for the utilization of D-lactate (8, 11). In S. cerevisiae it was suggested that D-LDH is involved in the metabolism of methylglyoxal (MG) (12).In eukaryotic cells, D-lactate results from the glyoxalase system (13,14). This system is the main MG catabolic pathway, comprising the enzymes glyoxalase I (lactoylglutathione lyase, EC 4.4.1.5) and glyoxalase II (hydroxyacylglutathione hydrolase, EC 3.1.2.6). MG (CH 3 -CO-CHO; see structure in Fig. 4) is a cytotoxic compound formed primarily as a by-product of glycolysis through nonenzymatic phosphate elimination from dihydroxyacetone phosphate and glyceraldehyde 3-phosphate (15), and its production in various plants is enhanced under stress conditions such as salt, drought, cold, and heavy metal stress (16,17). Moreover, the overexpression of glyoxalase I or II was shown to confer resistance to salt stress in tobacco and rice (17,18). It is assumed that the role of the MG pathway, from MG synthase to D-lactate cytochrome c oxidoreductase in the extant metabolism, is to detoxify MG, whereas in the early state of metabolic development it might function as an anaplerotic route for the tricarboxylic acid cycle (15). *

Plant d-2-Hydroxyglutarate Dehydrogenase Participates in the Catabolism of Lysine Especially during Senescence

“…Screening for T-DNA Insertion Lines and Genotyping-Homozygous plants of the T-DNA insertion line Salk_061383 (d2hgdh1-1) were obtained in a previous work (11). Seeds of the T-DNA insertion line GABI_127F12 (d2hgdh1-3) was obtained from the Nottingham Arabidopsis Stock Center.…”

“…Recently, we identified the D-2HGDH from Arabidopsis thaliana and characterized it at the biochemical level (11). This enzyme catalyzes the exclusive conversion of D-2HG to 2OG, which can enter the TCA cycle, whereas electrons are transferred to the electron transport chain through the ETF-ETFQO complex (1,11).…”

“…This enzyme catalyzes the exclusive conversion of D-2HG to 2OG, which can enter the TCA cycle, whereas electrons are transferred to the electron transport chain through the ETF-ETFQO complex (1,11). As gene coexpression analysis indicated that D-2HGDH is in the same network as several genes involved in ␤-oxidation and degradation of amino acids and chlorophyll, it was proposed that D-2HGDH participates in the catabolism of D-2HG most probably during the mobilization of alternative substrates from proteolysis and/or lipid degradation (11).…”

Characterization of the Branched-Chain Amino Acid Aminotransferase Enzyme Family in Tomato

“…Catabolism is believed to be initiated in mitochondria, where the branched-chain keto acid (BCKA) dehydrogenase complex is located (Taylor et al, 2004). The primary fates of BCAAs in plant cells are peptide elongation, glutamate recycling, Glc-and Suc-linked branched-chain esters, branched-chain fatty acid synthesis, and respiration through the synthesis of tricarboxylic acid cycle intermediates (Kandra et al, 1990;Walters and Steffens, 1990;Kroumova et al, 1994;Daschner et al, 1999;Li et al, 2003;Beck et al, 2004;Taylor et al, 2004;Engqvist et al, 2009). BCAA catabolism likely has other functions in plant metabolism.…”

Acrolein, an α,β-Unsaturated Carbonyl, Inhibits Both Growth and PSII Activity in the CyanobacteriumSynechocystissp. PCC 6803

“…AKR also reduces MG to acetol, with NAD(P)H as electron donor. [32][33][34] Gene expression of both glyoxalase and AKR is stimulated in response to salt, osmotic, and heat stress. 35,36) Additionally, the activity of AKR increases on exposure to drought stress.…”