title: Cell wall-associated malate dehydrogenase activity from maize roots.
abstract: Isolated cell walls from maize (Zea mays L.) roots exhibited ionically and covalently bound NAD-specific malate dehydrogenase activity. The enzyme catalyses a rapid reduction of oxaloacetate and much slower oxidation of malate. The kinetic and regulatory properties of the cell wall enzyme solubilized with 1M NaCl were different from those published for soluble, mitochondrial or plasma membrane malate dehydrogenase with respect to their ATP, Pi, and pH dependence. Isoelectric focusing of ionically-bound proteins and specific staining for malate dehydrogenase revealed characteristic isoforms present in cell wall isolate, different from those present in plasma membranes and crude homogenate. Much greater activity of cell wall-associated malate dehydrogenase was detected in the intensively growing lateral roots compared to primary root with decreased growth rates. Presence of Zn(2+) and Cu(2+) in the assay medium inhibited the activity of the wall-associated malate dehydrogenase. Exposure of maize plants to excess concentrations of Zn(2+) and Cu(2+) in the hydroponic solution inhibited lateral root growth, decreased malate dehydrogenase activity and changed isoform profiles. The results presented show that cell wall malate dehydrogenase is truly a wall-bound enzyme, and not an artefact of cytoplasmic contamination, involved in the developmental processes, and detoxification of heavy metals.
authors: Institute for Multidisciplinary Research, Kneza Višeslava 1, Belgrade, Serbia.
authors: Vesna
authors: V
authors: Hadži-Tašković Šukalović
authors: Mirjana
authors: M
authors: Vuletić
authors: Ksenija
authors: K
authors: Marković
authors: Zeljko
authors: Z
authors: Vučinić
mesh_terms: D002473:Cell Wall / Q000187:drug effects / Q000201:enzymology*; D003300:Copper / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration / Q000187:drug effects; D007525:Isoelectric Focusing; D007527:Isoenzymes / Q000302:isolation & purification / Q000378:metabolism; D007700:Kinetics; D008291:Malate Dehydrogenase / Q000302:isolation & purification / Q000378:metabolism*; D008293:Malates / Q000378:metabolism; D010071:Oxaloacetates / Q000378:metabolism; D010084:Oxidation-Reduction / Q000187:drug effects; D018517:Plant Roots / Q000166:cytology* / Q000187:drug effects / Q000201:enzymology*; D011485:Protein Binding / Q000187:drug effects; D012995:Solubility / Q000187:drug effects; D013347:Subcellular Fractions / Q000187:drug effects / Q000201:enzymology; D003313:Zea mays / Q000166:cytology* / Q000187:drug effects / Q000201:enzymology* / Q000254:growth & development; D015032:Zinc / Q000494:pharmacology
chemical_list: D007527:Isoenzymes; D008293:Malates; D010071:Oxaloacetates; D003300:Copper; C030298:malic acid; D008291:Malate Dehydrogenase; D015032:Zinc