title: Inhibition of 5-amino levulinic acid dehydratase activity by arsenic in excised etiolated maize leaf segments during greening.
abstract: In vivo as well as in vitro supply of sodium arsenate inhibited the 5-Amino levulinic acid dehydratase (5-aminolevulinate-hydrolyase EC 4.2.1.24, ALAD) activity in excised etiolated maize leaf segments during greening. The percent inhibition of enzyme activity by arsenate (As) was reduced by the supply of KNO3, but it was increased by the glutamine and GSH. Various inhibitors, such as, chloramphenicol, cycloheximide and LA, decreased the % inhibition of enzyme activity by As. The % inhibition of enzyme activity was also reduced by in vivo supply of DTNB. The enzyme activity was reduced substantially by in vitro inclusion of LA, both in the absence and presence of As. In vitro inclusion of DTNB and GSH inhibited the enzyme activity extracted from leaf segments treated without arsenate (-As enzyme) and caused respectively no effect and stimulatory effect on arsenate treated enzyme (+As enzyme). Increasing concentration of ALA during assay increased the activity of -As enzyme and +As enzyme to different extent, but double reciprocal plots for both the enzymes were biphasic and yielded distinct S0.5 values for the two enzymes (-As enzyme, 40 micromol/L and +As enzyme, 145 micromol/L) at lower concentration range of ALA only. It is suggested that As inhibits ALAD activity in greening maize leaf segments by affecting its thiol groups and/or binding of ALA to the enzyme.
authors.affiliation: School of Biochemistry, Devi Ahilya University, Takshashila Campus, Khandwa Road, Indore 452 017, India.
authors.forename: Meeta
authors.initials: M
authors.lastname: Jain
authors.forename: Rekha Puranik
authors.initials: RP
authors.lastname: Gadre
mesh_terms: D000622:Aminolevulinic Acid / Q000494:pharmacology; D001149:Arsenates / Q000633:toxicity; D001151:Arsenic / Q000633:toxicity*; D004228:Dithionitrobenzoic Acid / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000633:toxicity; D005978:Glutathione / Q000494:pharmacology; D066298:In Vitro Techniques; D007700:Kinetics; D007982:Levulinic Acids / Q000494:pharmacology; D009566:Nitrates / Q000494:pharmacology; D018515:Plant Leaves / Q000187:drug effects / Q000201:enzymology; D000623:Porphobilinogen Synthase / Q000037:antagonists & inhibitors*; D017680:Potassium Compounds / Q000494:pharmacology; D003313:Zea mays / Q000187:drug effects* / Q000201:enzymology* / Q000378:metabolism
chemical_list: D001149:Arsenates; D004791:Enzyme Inhibitors; D007982:Levulinic Acids; D009566:Nitrates; D017680:Potassium Compounds; C009277:sodium arsenate; D000622:Aminolevulinic Acid; D004228:Dithionitrobenzoic Acid; D000623:Porphobilinogen Synthase; D005978:Glutathione; D001151:Arsenic; C023844:potassium nitrate; C032246:levulinic acid