title: Expression and properties of the glyoxysomal and cytosolic forms of isocitrate lyase in Amaranthus caudatus L.
abstract: Isocitrate lyase (EC 4.1.3.1) catalyzes the reversible conversion of d-isocitrate to succinate and glyoxylate. It is usually associated with the glyoxylate cycle in glyoxysomes, although the non-glyoxysomal form has been reported and its relation to interconversion of organic acids outside the glyoxylate cycle suggested. We investigated the expression of two isocitrate lyase genes and activities of the glyoxysomal (ICL1) and cytosolic (ICL2) forms of isocitrate lyase in amaranth (Amaranthus caudatus L.) seedlings. Both forms were separated and purified. The cytosolic form had a low optimum pH (6.5) and was activated by Mn(2+) ions, while Mg(2+) was ineffective, and had a lower affinity to d, l-isocitrate (Km 63 μM) as compared to the glyoxysomal form (optimum pH 7.5, K(m) 45 μM), which was activated by Mg(2+). The highest ICL1 activity was observed on the 3rd day of germination; then the activity and expression of the corresponding gene decreased, while the activity of ICL2 and gene expression increased to the 7th day of germination and then remained at the same level. It is concluded that the function of ICL1 is related to the glyoxylate cycle while ICL2 functions independently from the glyoxylate cycle and interconverts organic acids in the cytosol.
authors.affiliation: Department of Biochemistry and Cell Physiology, Voronezh State University, Voronezh 394006, Russia.
authors.forename: Alexander T
authors.initials: AT
authors.lastname: Eprintsev
authors.affiliation: Department of Biochemistry and Cell Physiology, Voronezh State University, Voronezh 394006, Russia.
authors.forename: Dmitry N
authors.initials: DN
authors.lastname: Fedorin
authors.affiliation: Department of Biochemistry and Cell Physiology, Voronezh State University, Voronezh 394006, Russia.
authors.forename: Alexei V
authors.initials: AV
authors.lastname: Salnikov
authors.affiliation: Department of Biology, Memorial University of Newfoundland, St. John's, NL A1B 3X9, Canada. Electronic address: igamberdiev@mun.ca.
authors.forename: Abir U
authors.initials: AU
authors.lastname: Igamberdiev
mesh_terms: D027721:Amaranthus / Q000201:enzymology* / Q000235:genetics*; D001483:Base Sequence; D002499:Centrifugation, Density Gradient; D003600:Cytosol / Q000201:enzymology*; D018076:DNA, Complementary / Q000235:genetics; D004587:Electrophoresis, Agar Gel; D015971:Gene Expression Regulation, Enzymologic; D018506:Gene Expression Regulation, Plant; D017343:Genes, Plant; D018525:Germination; D020676:Glyoxysomes / Q000201:enzymology*; D006863:Hydrogen-Ion Concentration; D007522:Isocitrate Lyase / Q000235:genetics* / Q000302:isolation & purification / Q000378:metabolism; D007527:Isoenzymes / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D008969:Molecular Sequence Data; D020648:Peptide Elongation Factor 1 / Q000378:metabolism; D036226:Seedlings / Q000201:enzymology; D013347:Subcellular Fractions / Q000201:enzymology
chemical_list: D018076:DNA, Complementary; D007527:Isoenzymes; D020648:Peptide Elongation Factor 1; D007522:Isocitrate Lyase
keywords: Amaranthus caudatus; Cytosol; Glyoxylate cycle; Glyoxysome; Isocitrate lyase