Association Constants of Methylmercuric and Mercuric Ions with Nucleosides

Simpson, Richard B.

doi:10.1021/ja01064a029

Cited by 211 publications

(79 citation statements)

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“…In order to understand better which adenine atoms are involved in the binding to the enzyme, difference spectra measurements were taken of ATP, adenosine and I-methyl adenosine. The chemical probe, CH,HgOH, has been shown by ultraviolet [9] and by Raman spectroscopic studies [lo, 1 11 to bind to specific sites of the adenosine moiety. Formaldehyde, which specifically reacts with the -NH, group of the adenosine moiety [12, 131, was also used.…”

Section: Ultraviolet Difference Spectroscopymentioning

confidence: 99%

Baker's Yeast Adenlate Kinase

Tomasselli

Noda

1983

European Journal of Biochemistry

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(ATPPS) were used to determine the stereochemical mode of coordination of Mg2+ to ATP when bound in the yeast adenylate kinase complex. ATPaS isomer A is the preferred substrate either in the presence of Mg" or Cd2+ ; ratios of the rate of reaction at infinite concentration of substrate, V, for A to B isomers of ATPclS with MgZ + were 457/51.4 = 8.9 and with CdZC 124/12.8 = 9.7. Thus there is no reversal of stereospecificity on substituting Cd2+ for Mg2+ and this supports the view that metal does not chelate with the a-P. In contrast the V ratios of ATPPS(A) to ATPPS(B) withMg2+ were 1.33/0.15 = 8.9 andwithCd" O.lSj5.l = 0.035.Thusthisreversal ofstereospecificitywhenCd'+ is substituted for MgL + (in view of the fact that Mg2 + binds to 0 and Cd2+ to S) leads to the conclusion that a metal chelation must occur via the p-phosphate. Since the enzyme prefers MgATPPS(A) and CdATPPS(B) (both isomers have A-screw sense) to MgATPpS(B) and CdATPPS(A) (both isomers have A-screw sense) and Mg2+ also coordinates with the y-phosphate (by analogy with other adenylate kinase isozymes), the interpretation is that baker' yeast adenylate kinase binds MgATP as A , P, y. The fluorescence of the two Trp residues of yeast adenylate kinase has been used to investigate conformational changes of the enzyme on binding its substrates. Fluorescence is maximal at 334 nm (A,,, 295 nm, pH 7.5) and is reduced 10 % with no shift in A, , , in the presence of ATP and reduced a further 15 % on the addition of Mg2+ or other metal acitvators to E-ATP. In contrast non-activating metals such as Ba2+ and Sr2+ increase quenching only slightly. With ITP, UTP, CTP, GTP the quenching is 4.1 %, 5.2 %, 8.7 % and 6.6 % with or without MgL +. Differential conformational changes ofyeast adenylate kinase on binding MgATP, ATP, and other nucleotides are shown by (a) fluorescence changes, (b) previously reported kinetic and binding studies and (c) by the fact that the K , for AMP in the presence of MgATP is 17 times less than in the presence of MgGTP. These differential conformational changes result in differing tendencies of AMP to bind to the enzyme. Ultraviolet difference spectra obtained on binding of ATP to the enzyme (shoulder at 271 nm and peak at 276 nni) have been compared with the difference spectra of the interaction of ATP, adenosine and I-methyl adenosine respectively with methyl mercuric hydroxide and formaldehyde. On the basis of these comparisons, the shoulder at 271 nm reflects the interaction of N(l) and the peak at 276 nm the interaction of the 6-amino group of ATP with the enyzme.The following mechanism of reaction is proposed : upon binding MgATP the enzyme undergoes a conformational change which closes the active-site crevice by bringing the two lobes closer, expelling water from the crevice. AMP is bound with higher affinity and the a-oxygen attacks the y-phosphate of ATP in a nucleophilic reaction. correct and complete conformational change necessary for an appropriate binding of AMP at the AMP site and to give maximal activity; (c) nucleot...

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Section: Ultraviolet Difference Spectroscopymentioning

confidence: 99%

Baker's Yeast Adenlate Kinase

Tomasselli

Noda

1983

European Journal of Biochemistry

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“…Recent measurements of Raman spectra of CH3Hg(II) complexes of a mixture of nucleotides representing the base composition of CT-DNA are interpreted to represent sequential binding to N3 of UMP and N1 of GMP (15), which follows the predicted order ofsite affinities (1,3). No binding to N7of GM P was detected, however.…”

Section: Resultsmentioning

confidence: 99%

Methylmercury(II) binding to single-stranded and duplex DNA: complexes formed are distinguishable by optical detection of magnetic resonance spectroscopy.

Maki¹,

Ott²

1981

Proc. Natl. Acad. Sci. U.S.A.

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Binding of CH3Hg(II) to duplex and singlestranded calf thymus DNA leads to an external heavy atom effect that is associated with the formation ofcomplexes directly with the purine and pyrimidine bases. When CH3Hg(II) is added at a concentration insufficient to cause denaturation, clearly distinguishable optical detection of magnetic resonance spectra are observed from the duplex and single-stranded DNA complexes. Comparison of the dominant signals with those observed from CH3Hg(II) complexes of model mononucleotides and mononucleosides allows their identification as guanine complexed at N7 in the duplex sample and thymine complexed at N3 in the single-stranded sample. On the basis of these measurements, it is estimated that this experiment presently is capable of detecting about 2% singlestranded DNA in a sample made up predominantly of the duplex structure. Methylmercury, CH3Hg(II), is known to bind to the bases of DNA (1, 2). When added at sufficient concentration, which depends upon such factors as temperature, base composition, and the pH and ionic strength of the buffer, CH3Hg(II) causes denaturation of duplex DNA (3,4). CH3Hg(II) binds more strongly to N than to 0 atoms and coordinates tightly with only one ligand; thus, unlike Ag(I), which binds to two ligands in linear coordination, CH3Hg(II) is not expected to crosslink DNA bases. At pH near 7, CH3Hg(II) coordinates most strongly at. the N3 site of thymine and somewhat less tightly at the N1 site ofguanine (1, 3). These atoms are involved in Watson-Crick base pairing of the DNA duplex and thus are not accessible to complexing with CHjHg(II) in the absence of disruption of the base pairing. The coordination chemistry of CH3Hg(II) is consistent, therefore, with the observation (3, 4) that while singlestranded DNA binds CH3Hg(II) noncooperatively at low CH3Hg(II) concentrations, no complexing with duplex DNA is observed until a critical concentration is reached, whereupon massive binding occurs cooperatively, accompanied by denaturation of the DNA. Ag(I), on the other hand, forms complexes at very low concentrations with duplex DNA in the absence of denaturation (5, 6). Release ofprotons that accompanies binding suggests that Ag(I) may replace protons in the base pairs and form linear complexes between complementary bases.We have recently studied-(7) the complexes formed by CH3Hg(II) with duplex calf thymus DNA (CT-DNA), using optical detection of triplet state magnetic resonance (ODMR) spectroscopy. Complexes were formed by equilibrium dialysis at CH3Hg(II) concentrations insufficient to cause denaturation. In this application of ODMR we were able to take advantage of the heavy atom effect (8) induced by the Hg atom to selectively detect ODMR signals from complexed bases. ComparisonThe publication costs of-this article were defrayed in part by page charge payment. This article must therefore be hereby marked "advertisement" in accordance with 18 U. S. C. §1734 solely to indicate this fact.ofthe ODMR spectra with those of CH3Hg(II).mononucleotide ...

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“…A DNA base crosslinked with Hg 2+ would prevent RNA polymerases from dividing the sense and antisense DNA strands, which precedes nascent mRNA synthesis. Although methylmercury ion (MeHg + ) also binds to various nucleotides with comparable affinity to that of Hg 2+ (Simpson, 1964), MeHg + cannot form a crosslink due to the occupation of a binding site with a methyl group. Thus, MeHg + is unable to affect DNA conformation and gene expression.…”

Section: Dna/rna Strand Modification and Gene Expression Inhibitionmentioning

confidence: 99%

Effects of organic and inorganic mercury(II) on gene expression via DNA conformational changes

Ueda

Makino

Tobe

et al. 2014

Fundam. Toxicol. Sci.

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-The effects of organic and inorganic mercury ions on gene expression were studied by in vitro cell-free assays for transcription and translation. While organic mercury (methylmercury chloride, MeHgCl) showed no effects, treatment of template DNA with inorganic mercury (HgCl 2 ) inhibited mRNA synthesis in a bacteriophage T7 RNA polymerase transcription system. The inhibited transcription resulted in reduced protein synthesis after the subsequent application of the transcripts to a translation system consisting of Sf21 insect cell lysate. Treatment of mRNA with inorganic mercury also reduced translation, although this inhibitory effect was weaker than the effect produced by DNA exposure. Treatment of DNA and RNA with mercury did not increase oxidative damage such as strand cleavage and base oxidation. Instead, circular dichroism spectrometry demonstrated that mercury ions, not methyl mercury, drastically changed strand conformation of DNA and RNA. Therefore, the gene expression inhibition observed in this study was thought to be caused by crossbridging of DNA bases with mercury ions, which blocked the transcriptional machinery. Taken together with reports on biological conversion of organic mercury to inorganic forms in animals, our results show that transcriptional inhibition via conformational changes in DNA could be a toxic mechanism involved in mercury poisoning.

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Association Constants of Methylmercuric and Mercuric Ions with Nucleosides

Cited by 211 publications

References 0 publications

Baker's Yeast Adenlate Kinase

Baker's Yeast Adenlate Kinase

Methylmercury(II) binding to single-stranded and duplex DNA: complexes formed are distinguishable by optical detection of magnetic resonance spectroscopy.

Effects of organic and inorganic mercury(II) on gene expression via DNA conformational changes

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