title: Protective effects of Ca2+, Mg2+, Cu2+, and Ni2+ on mercury and methylmercury toxicity to a cyanobacterium.
abstract: Toxicological investigations of the impact of inorganic mercury (Hg2+) and methylmercury (CH3Hg+) in terms of growth, NH4+ uptake, in vivo glutamine synthetase (transferase) activity, and regulation of toxicity by Ca2+, Mg2+, Cu2+ and Ni2+ in the diazotrophic cyanobacterium Nostoc calcicola Bréb. have been completed. Photoautotrophic growth of the cyanobacterium was extremely sensitive to both mercury compounds, CH3Hg+ being 2.5 times more toxic than Hg2+. Although NH4+ uptake was 6 times more sensitive than in vivo GS activity against the two mercurials, both processes had a greater susceptibility toward CH3Hg+. On the basis of Km and Vmax, it is suggested that both mercury species inhibit such metabolic events noncompetitively. Ca2+, Mg2+, Cu2+, and Ni2+ did not change the nature of inhibition and effectively antagonized the Hg2+ and CH3Hg+ toxicities in the sequence Ca2+ greater than Mg2+ much greater than Cu2+ greater than Ni2+.
authors.affiliation: Algal Research Laboratory, Centre of Advanced Study in Botany, Banaras Hindu University, Varanasi, India.
authors.forename: C B
authors.initials: CB
authors.lastname: Singh
authors.forename: S P
authors.initials: SP
authors.lastname: Singh
mesh_terms: D002118:Calcium / Q000494:pharmacology; D002455:Cell Division / Q000187:drug effects; D003300:Copper / Q000494:pharmacology; D000458:Cyanobacteria / Q000187:drug effects* / Q000201:enzymology / Q000502:physiology; D005974:Glutamate-Ammonia Ligase / Q000037:antagonists & inhibitors / Q000378:metabolism; D008658:Inactivation, Metabolic; D007700:Kinetics; D008274:Magnesium / Q000494:pharmacology; D008628:Mercury / Q000633:toxicity*; D008670:Metals / Q000494:pharmacology*; D008767:Methylmercury Compounds / Q000493:pharmacokinetics / Q000633:toxicity*; D009532:Nickel / Q000494:pharmacology; D010788:Photosynthesis; D000644:Quaternary Ammonium Compounds / Q000493:pharmacokinetics; D012680:Sensitivity and Specificity
chemical_list: D008670:Metals; D008767:Methylmercury Compounds; D000644:Quaternary Ammonium Compounds; D003300:Copper; D009532:Nickel; D005974:Glutamate-Ammonia Ligase; D008628:Mercury; D008274:Magnesium; D002118:Calcium