Expression and properties of the mitochondrial and cytosolic forms of aconitase in maize scutellum.
Aconitase (EC 4.2.1.3) catalyzes the reversible interconversion of citrate, cis-aconitate, and D-isocitrate. It operates in mitochondria and cytosol. We investigated the expression of two aconitase genes (Aco1 and Aco4) and activities of the mitochondrial and cytosolic forms in maize (Zea mays L.) scutellum during germination. Both forms were isolated and purified. The cytosolic form had a higher pH optimum (8.0), twice higher affinity to citrate (K(m) 9.5 mM), and slightly lower affinity to D,L-isocitrate (K(m) 1.7 mM) as compared to the mitochondrial form (optimum pH 7.5, K(m) with citrate 21 mM, and K(m) with isocitrate 1.5 mM). The highest activity of both forms of aconitase was observed on the 4th day of germination; then the activity and expression of the cytosolic form sharply decreased, while the mitochondrial form decreased more slowly. The mitochondrial aconitase was more strongly inhibited by H2O2 (half-inhibition at 35 μM) than the cytosolic form (60 μM). Aconitase activity was not detected in the glyoxysomal fraction beyond the cross-contamination level. It is suggested that the mitochondrial form operates in the tricarboxylic acid cycle, whereas the cytosolic form participates in the reactions of the glyoxylate cycle taking place outside the glyoxysome.
Department of Biochemistry and Cell Physiology, Voronezh State University, Voronezh 394006, Russia.
Alexander T
AT
Eprintsev
Department of Biochemistry and Cell Physiology, Voronezh State University, Voronezh 394006, Russia.
Dmitry N
DN
Fedorin
Department of Biochemistry and Cell Physiology, Voronezh State University, Voronezh 394006, Russia.
Marina V
MV
Nikitina
Department of Biology, Memorial University of Newfoundland, St. John's, NL A1B 3X9, Canada. Electronic address: igamberdiev@mun.ca.
Abir U
AU
Igamberdiev
D000154:Aconitate Hydratase / Q000235:genetics* / Q000302:isolation & purification / Q000378:metabolism; D003600:Cytosol / Q000201:enzymology*; D015971:Gene Expression Regulation, Enzymologic; D018506:Gene Expression Regulation, Plant; D017343:Genes, Plant; D018525:Germination; D020676:Glyoxysomes / Q000201:enzymology; D006863:Hydrogen-Ion Concentration; D007527:Isoenzymes / Q000378:metabolism; D007700:Kinetics; D008928:Mitochondria / Q000201:enzymology*; D013347:Subcellular Fractions / Q000201:enzymology; D003313:Zea mays / Q000033:anatomy & histology / Q000201:enzymology* / Q000235:genetics*
D007527:Isoenzymes; D000154:Aconitate Hydratase
Aconitase; Glyoxylate cycle; Mitochondria; Scutellum; Zea mays