scholarly journals Gluconeogenesis in Plants: A Key Interface between Organic Acid/Amino Acid/Lipid and Sugar Metabolism

Molecules ◽  
2021 ◽  
Vol 26 (17) ◽  
pp. 5129
Author(s):  
Robert P. Walker ◽  
Zhi-Hui Chen ◽  
Franco Famiani
Keyword(s):  
Enzyme Activity ◽  
Malic Enzyme ◽  
Krebs Cycle ◽  
Cytosolic Ph ◽  
Widespread Occurrence ◽  
Nitrogenous Compounds ◽  
Coordinate Regulation ◽  
Fine Control ◽  
Malate Metabolism

Gluconeogenesis is a key interface between organic acid/amino acid/lipid and sugar metabolism. The aims of this article are four-fold. First, to provide a concise overview of plant gluconeogenesis. Second, to emphasise the widespread occurrence of gluconeogenesis and its utilisation in diverse processes. Third, to stress the importance of the vacuolar storage and release of Krebs cycle acids/nitrogenous compounds, and of the role of gluconeogenesis and malic enzyme in this process. Fourth, to outline the contribution of fine control of enzyme activity to the coordinate-regulation of gluconeogenesis and malate metabolism, and the importance of cytosolic pH in this.

scholarly journals YtsJ Has the Major Physiological Role of the Four Paralogous Malic Enzyme Isoforms in Bacillus subtilis

2006 ◽  
Vol 188 (13) ◽  
pp. 4727-4736 ◽  
Author(s):  
Guillaume Lerondel ◽  
Thierry Doan ◽  
Nicola Zamboni ◽  
Uwe Sauer ◽  
Stéphane Aymerich
Keyword(s):  
Enzyme Activity ◽  
Bacillus Subtilis ◽  
Malic Enzyme ◽  
Metabolic Flux ◽  
Physiological Role ◽  
Extreme Case ◽  
Growth Defect ◽  
Flux Analysis ◽  
Malic Enzyme Activity

ABSTRACT The Bacillus subtilis genome contains several sets of paralogs. An extreme case is the four putative malic enzyme genes maeA, malS, ytsJ, and mleA. maeA was demonstrated to encode malic enzyme activity, to be inducible by malate, but also to be dispensable for growth on malate. We report systematic experiments to test whether these four genes ensure backup or cover different functions. Analysis of single- and multiple-mutant strains demonstrated that ytsJ has a major physiological role in malate utilization for which none of the other three genes could compensate. In contrast, maeA, malS, and mleA had distinct roles in malate utilization for which they could compensate one another. The four proteins exhibited malic enzyme activity; MalS, MleA, and MaeA exhibited 4- to 90-fold higher activities with NAD+ than with NADP+. YtsJ activity, in contrast, was 70-fold higher with NADP+ than with NAD+, with Km values of 0.055 and 2.8 mM, respectively. lacZ fusions revealed strong transcription of ytsJ, twofold higher in malate than in glucose medium, but weak transcription of malS and mleA. In contrast, mleA was strongly transcribed in complex medium. Metabolic flux analysis confirmed the major role of YtsJ in malate-to-pyruvate interconversion. While overexpression of the NADP-dependent Escherichia coli malic enzyme MaeB did not suppress the growth defect of a ytsJ mutant on malate, overexpression of the transhydrogenase UdhA from E. coli partially suppressed it. These results suggest an additional physiological role of YtsJ beyond that of malate-to-pyruvate conversion.

The regulation of oat coleoptile phosphoenolpyruvate carboxylase and malic enzyme activities by H+ and metabolites. Kinetic evidence for and against a metabolic pH-stat

1981 ◽  
Vol 59 (8) ◽  
pp. 1397-1404 ◽  
Author(s):  
Ceredwyn E. Smith ◽  
Alan W. Bown
Keyword(s):  
Enzyme Activity ◽  
Phosphoenolpyruvate Carboxylase ◽  
Malic Enzyme ◽  
Ph Regulation ◽  
Substrate Inhibition ◽  
Malic Enzyme Activity ◽  
Ph Stat ◽  
Phosphorylated Sugars ◽  
Cytosol Ph

Phosphoenolpyruvate carboxylase (EC 4.1.1.31) and malic enzyme (EC 1.1.1.40) activities in soluble protein extracts of Avena coleoptiles were investigated as functions of pH. The presence of malic enzyme activity was confirmed by radiochemical assays which identified the product of the forward reaction and spectrophotometric assays which demonstrated that reduction or oxidation of NADP required all the substrates and cofactors necessary for the forward or reverse reactions. In neither assay could NADP or Mn2+ be replaced by NAD or Mg2+. Activity was independent of pH (6.0 to 7.7) at malate concentrations less than 0.1 mM. At higher concentrations the pH increase raised activity by at least 100%, and substrate inhibition by malate resulted in activity at 0.97 mM malate which was less than that at 0.5 mM malate. The increase in malic enzyme activity with rising pH can be attributed to a decrease in substrate inhibition and a decrease in Km,app (Mn2+). pH increases between 7.0 and 7.6 increased Vmax and phosphoenolpyruvate limited phosphoenolpyruvate carboxylase (PEPC) activity by over 200%, and decreased the Km,app (Mg2+). Inhibition of PEPC and malic enzyme by various carboxylic acids and phosphorylated sugars decreased as the assay pH rose. The results are discussed in light of contrasting suggestions concerning the role of these enzymes in cytosol pH regulation.

Morphological and biochemical analyses of changes in rat hepatocytes related to wine and ethanol consumption

1984 ◽  
Vol 42 ◽  
pp. 232-233
Author(s):  
S.M. Geyer ◽  
C.L. Mendenhall ◽  
J.T. Hung ◽  
E.L. Cardell ◽  
R.L. Drake ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
Endoplasmic Reticulum ◽  
Enzyme Activity ◽  
Malic Enzyme ◽  
Smooth Endoplasmic Reticulum ◽  
Rat Hepatocytes ◽  
Mature Male ◽  
Treatment Groups ◽  
Malic Enzyme Activity ◽  
Biochemical Analyses

Thirty-three mature male Holtzman rats were randomly placed in 3 treatment groups: Controls (C); Ethanolics (E); and Wine drinkers (W). The animals were fed synthetic diets (Lieber type) with ethanol or wine substituted isocalorically for carbohydrates in the diet of E and W groups, respectively. W received a volume of wine which provided the same gram quantity of alcohol consumed by E. The animals were sacrificed by decapitation after 6 weeks and the livers processed for quantitative triglycerides (T3), proteins, malic enzyme activity (MEA), light microscopy (LM) and electron microscopy (EM). Morphometric analysis of randomly selected LM and EM micrographs was performed to determine organellar changes in centrilobular (CV) and periportal (PV) regions of the liver. This analysis (Table 1) showed that hepatocytes from E were larger than those in C and W groups. Smooth endoplasmic reticulum decreased in E and increased in W compared to C values.

scholarly journals The role of malic enzyme in the regulation of lipid accumulation in filamentous fungi

Microbiology ◽  
1999 ◽  
Vol 145 (8) ◽  
pp. 1911-1917 ◽  
Author(s):  
James P. Wynn ◽  
Aidil bin Abdul Hamid ◽  
Colin Ratledge
Keyword(s):  
Filamentous Fungi ◽  
Lipid Accumulation ◽  
Malic Enzyme
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