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Biological regulation often depends on reversible reactions such as phosphorylation, acylation, methylation, and glycosylation, but rarely halogenation. A notable exception is the iodination and deiodination of thyroid hormones. Here, we report detection of bromotyrosine and its subsequent debromination during Drosophila spermatogenesis. Bromotyrosine is not evident when Drosophila express a native flavin-dependent dehalogenase that is homologous to the enzyme responsible for iodide salvage from iodotyrosine in mammals. Deletion or suppression of the dehalogenase-encoding condet (cdt) gene in Drosophila allows bromotyrosine to accumulate with no detectable chloro-or iodotyrosine. The presence of bromotyrosine in the cdt mutant males disrupts sperm individualization and results in decreased fertility. Transgenic expression of the cdt gene in late-staged germ cells rescues this defect and enhances tolerance of male flies to bromotyrosine. These results are consistent with reversible halogenation affecting Drosophila spermatogenesis in a process that had previously eluded metabolomic, proteomic, and genomic analyses. [ABSTRACT FROM AUTHOR]

The detection and characterization of a kinetic product of (dA) alkylation helps to reconcile the contradiction between the strength of nucleophiles in DNA and their propensity for addition to a model quinone methide. The thermodynamic stability of the individual adducts rather than the kinetics of their formation appears to control the profile of detectable products and this also dominates the profiles of deoxyguanosine (dG) and deoxycytosine (dC) adducts.

Investigation of the selectivity of guanine oxidation promoted by nickel and cobalt reagents has been conducted by means of Z-DNA structural characteristics. Results demonstrate the possibility of the reagent application to different targets.

A macrocyclic nickel complex and selective association with extrahelical guanine residues are discussed. The proximity of the guanines brings on composite paramagnetic effects that affect each adjacent nucleotide by direct and proximal coordination of nickel

Research was conducted to examine the alkylation of nucleic acids by a model quinone methide. A stable model compound, O-(tert-butyldimethylsilyl)-2-bromomethylphenol, was used to characterize the intrinsic reactivity of the species by generating an o-quinone methide in the presence of fluoride. Results indicate the ability of the exo-amine group of guanine to maintain its reactivity most effectively from nucleoside to helical DNA.

The mechanism and application of nucleic acid probes based on macrocylic complexes of nickel were examined. Guanine N7 was relocated to the exterior of the helix after the conversion of DNA from a B- to Z-helix which resulted to better metal binding. Stabilization of the Z-DNA was achieved due to the presence of a kinetically accessible coordination site within a nickel complex. It was also noted that the nucleic acid structure was not altered as a result of the association between nickel intermediates and accessible guanines.

Nickel- and cobalt-dependent reagents were used to elucidate the structure of RNA that are not discovered by other enzymatic probes, such as dimethyl sulphate. The average reactivity of G675 and insignificant reactivity with RNase T1 confirmed the structural model of loop E, similarly determined from other physical methods. The tetraloop structure of loop D was also more evident from the reactivity of G87 and G89, when the nickel reagent was used compared to RNase T1.

The modification of deoxyribonucleic acid was achieved by reacting either a single-stranded oligodeoxynucleotide or a 17-base haipin-forming oligodeoxynucleotide with KHSO5 and a metal catalyst, CoCl2, under conditions of high temperature. The reaction, which also involved piperidine treatment, demonstrated that the reactivity of CoCl2 is nearly double that of NiCR where CR = 2,12-dimethyl-3,7,11,17-tetraazobicyclo(11.3.1)heptadeca-1(17),2,11,13,15-pe ntaene.

Oligonucleotide-naphthoquinone conjugates are inducible, site-directed agents in the sequence-specific alkylation of DNA. Either biomimetic reduction or near-UV radiation mediates the reaction and involves formation of a transient, electrophilic quinone methide intermediate. The alkylation targets are guanine and cytosine.

The oxidation rates of oligonucleotide duplexes consisting of complementary, mispaired and unpaired bases were estimated and compared to explore the enhancement of the solvent exposure of the reactive carbon-carbon (C5-C6) double bond of the base of certain thymine residues. The preferential oxidation of these residues has been linked to unwinding, unpairing or unstacking of the base that enhances solvent exposure. The alteration of polyanionic DNA by the anionic oxidant permanganate is regulated by a powerful electrostatic component.

The confirmation-specific oxidation of guanosine in polynucleotide RNA is promoted by a nickel complex. The solvent exposure and surface properties of guanine N7 affect the reaction with the RNA. The crystal structure of yeast is used as a foundation to study G18, G19, G20 and Gm34, which reveals the changes in the native tRNA (Phe) (yeast). The tRNA unfolds when Mg2+ is not present, exposing the guanine derivatives to oxygen. The guanosine residues in haripin loops and duplex terminuses and the necessary cofactor binding site are revealed by the reaction sugar backbone and base position in guanosine residues. Intron RNA and tRNA (Phe) are characterized by the nickel complex found in polynucleotide RNA.

The introduction of tetraazamacrocyclic ligands improves the performance of the ligand-dependent nickel(II) (Ni) complexes in inducing DNA oxidation utilizing KHSO5 as oxidant. However, the flexibility of the complex to adapt to DNA binding influences the degree of its DNA reactivity. Furthermore, the reactivity and specificity of the Ni(II) complexes have been determined using the 17-base hairpin oligonucleotide d(AGTCTATGGGTTAGACT). The different ligands have provided data regarding the reaction of the Ni(II) with DNA molecules.

The active-site nucleophile, Ser-102, can be replaced with leucine or alanine, and still perform as a functional enzyme in phosphate monoester hydrolysis. The two mutant enzymes, Ala-102 and Leu-102, possess many steady-state kinetic properties similar to wild-type enzymes. Moreover, the site-directed mutagenesis supports the importance of zinc atom presence in the active site of bacterial alkaline phosphatase.

Aberrant guanine positions in the DNA helix, such as mispairs, bulges, loops and terminal residues, may now be detected by selective oxidation with Ni(II) macrocyclic complex in the presenceof KHSO4. The metal-based reagent spares all the other bases including properly-paired guanines and guanines protected by complementary pairs and stacks. The oxidized guanines are identified after a piperidine-induced splitting of the DNA strand.

The nature of the reaction pathway and the ability of the reactive intermediate to dissociate with the helical conformations regulated the specificity of DNA alkylation. Nuclear magnetic resonance-bases analysis of quinone methide precursors that induce the selective alkylation of DNA indicated the role of the N3 nitrogen unit of the cross-linking DNA in mediating reactions with the methide precursor. Furthermore, the N3 cyclic nitrogen was modified by the intrinsic selectivity of the quinone methide.

A study of iodotyrosine deiodinase enzyme which promoted a net reductive deiodination of 3-iodotyrosine to form iodide and tyrosine to regulate iodide homeostasis and proper thyroid function in mammals is reported. The activity of enzyme deiodinase to act as a debrominase and a dechlorinase expanded the possible roles of flavin in biological catalysis and provided a foundation for determining the mechanism underlying unusual process of dehalogenation.

The activation of hydrogen peroxide and dioxygen by the dinuclear copper complexes in an aqueous solution is discussed. The internal electron transfer from the ligand is shown to initiate the production of hydroxyl radical in the system.

Self-repair of thymine dimer in duplex DNA was studied. Dimerization of thymine results in cyclobutane dimer which influences the repair mechanism in DNA.

A phenolate-containing binucleating ligand PD'OH was employed to synthesize a dinuclear copper complex ([[Cu.sup.II.sub.2](PD'[O.sup.-]([H.sub.2]O)].sup.3+] and characterize it structurally and spectroscopically. This complex promoted selective oxidation of guanine residues at ss/ds junctions in the presence of MPA and [O.sub.2] and the reaction was most efficient when a minimum of two Gs flanked each of the 3'- and 5'- extensions from the duplex junction.