title: Using electrospray ionization mass spectrometry to explore the interactions among polythymine oligonucleotides, ethidium bromide, and mercury ions.
abstract: We have used electrospray ionization mass spectrometry (ESI-MS) and fluorescence and circular dichroism (CD) spectroscopy to explore the binding of ethidium bromide (EthBr) to non-self-complementary polythymine (polyT) strands in the absence and presence of Hg2+ ions. In the gas phase, ESI-MS revealed that Hg2+ ions have greater affinity, through T-Hg2+-T coordination, toward polyT strands than do other metal ions. These findings are consistent with our fluorescence and CD results obtained in solution; they revealed that more T33-EthBr-Hg2+ complexes existed upon increasing the concentrations of Hg2+ ions (from 0 to 50 microM). Surprisingly, the ESI-MS data indicated that the Hg2+ concentration dependence of the interaction between T33 and EthBr is biphasic. Our ESI-MS data revealed that the T33-EthBr-Hg2+ complexes formed with various stoichiometries depending on their relative concentrations of the components and the length of the DNA strand. When the concentrations of T33/EthBr/Hg2+ were 5/5/2.5 microM and 5/10/7.5 microM, 1:1:1 and 1:1:2 T33-EthBr-Hg2+ complexes were predominantly formed, respectively. Thus, Hg2+-induced DNA conformational changes clearly affect the interactions between DNA and EthBr.
authors.affiliation: Department of Chemistry, National Taiwan University, Taipei, Taiwan.
authors.forename: Cheng-Kang
authors.initials: CK
authors.lastname: Chiang
authors.forename: Yang-Wei
authors.initials: YW
authors.lastname: Lin
authors.forename: Cho-Chun
authors.initials: CC
authors.lastname: Hu
authors.forename: Huan-Tsung
authors.initials: HT
authors.lastname: Chang
mesh_terms: D002412:Cations / Q000737:chemistry; D004996:Ethidium / Q000737:chemistry*; D008628:Mercury / Q000737:chemistry*; D019216:Metals, Heavy / Q000737:chemistry; D009690:Nucleic Acid Conformation; D011071:Poly T / Q000737:chemistry*; D013050:Spectrometry, Fluorescence; D021241:Spectrometry, Mass, Electrospray Ionization / Q000379:methods*
chemical_list: D002412:Cations; D019216:Metals, Heavy; D011071:Poly T; D004996:Ethidium; D008628:Mercury