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The solubility of lucigenin was measured in alcohols and aqueous alcohol mixtures. The solubility of lucigenin in normal alcohols exponentially decreased with increasing molecular weight of primary normal alcohols, whereas in alcohol–water mixtures it showed a maximum at specific alcohol concentrations. Solvent and bases effects on chemiluminescence (CL) of lucigenin have been investigated for methanol, ethanol, 1-propanol, 1-butanol, and aqueous mixtures of methanol and ethanol, and for various amine and alkaline metal bases, respectively. The CL intensities of lucigenin decreased in two-step processes: the main one with a short apparent lifetime of 0.3 ± 0.1 s and another one due to subreactions with a relatively long lifetime dependent on base concentration. At lower concentration of bases, the apparent CL lifetime increased in the order LiOH < NaOH < KOH. Both solvent and base effects on the solubility and CL of lucigenin are discussed from a standpoint of the amphipathic nature of lucigenin and solvents.

Abstract The product of the BLM gene, which is mutated in Bloom syndrome in humans, and the Saccharomyces cerevisiae protein Sgs1 are both homologous to the Escherichia coli DNA helicase RecQ, and have been shown to be involved in the regulation of homologous recombination. Mutations in these genes result in genome instability because they increase the incidence of deletions and translocations. We present evidence for a genetic interaction between SGS1 and YKU70, which encodes the S. cerevisiae homologue of the human DNA helicase Ku70. In a yku70 mutant background, sgs1 mutations increased sensitivity to DNA breakage induced either by treatment with camptothecin or by the expression of the restriction enzyme EcoRI. The yku70 mutation caused a fourfold increase in the rate of double-strand break (DSB)-induced target integration as that seen in the sgs1 mutant. The combination of yku70 and sgs1 mutations additively increased the rate of the targeted integration, and this effect was completely suppressed by deletion of RAD51. Interestingly, an extra copy of YKU70 partially suppressed the increase in targeted integration seen in the sgs1 single mutant. These results suggest that Yku70 modulates the repair of DSBs associated with homologous recombination in a different way from Sgs1, and that the inactivation of RecQ and Ku70 homologues may enhance the frequency of gene targeting in higher eukaryotes.

We have developed the utility of a pair of pyrene groups on L-1-pyrenylalanines (Pya) as a conformational probe for designed peptides composed of α-helices. Here, we expand the usefulness of the probing method to the antiparallel β-sheet structure formed in cyclic peptides. A pair of Pya residues were introduced into cyclic decapeptides, gramicidin S and its analogous peptide, at various positions which were involved in antiparallel β-sheet structures with amphiphilic character. When the two Pya residues were deployed on different β-strands, exciton interaction in circular dichroism spectra showed that the two pyrene rings were arranged with a left-handed twist. They were orientated in a right-handed sense on the same strand. The pyrene rings showed strong excimer emission. These results demonstrate that the behaviour of the pyrene probe is coincident with the left-handed orientation of two β-strands and the right-handed twist of a single β-strand in natural protein structures.

A gramicidin S (GS) analog ([Bpa2,2′]GS), in which the Orn residues are replaced by l-5-bipyridylalanines, was synthesized by the solid-phase-synthesis and cyclization-cleavage method. The analog formed stable 1:1 complexes with transition metal ions such as Co2+, Ni2+, Cu2+, and Zn2+in CH3OH without significant conformational change as shown by the 1H-NMR and circular dichroism analyses. These peptide-metal complexes are water-soluble and will be used in various models of artificial metalloproteins based on the β-sheet structure.

Two kinds of hydroxylamino-dinitrotoluenes (HADNTs), 2-hydroxylamino-4,6-dinitrotoluene (2HADNT) and 4-hydroxylamino-2,6-dinitrotoluene (4HADNT), are known to be major metabolites produced from 2,4,6-trinitrotoluene (TNT) by bacteria. These chemicals could not be identified as TNT metabolites produced by Pseudomonas sp. strain TM15 because the mass spectra of these chemicals could not be obtained by liquid chromatography-mass spectrometry (MS) or gas chromatography-MS, which are the classic methods for identifying the metabolites of xenobiotics. However, these problems are overcome by isolating 2HADNT and 4HADNT from TNT metabolites with one-step thin-layer chromatography using dichloromethane as the developing solvent, and individually extracting them into acetonitrile by collecting spots of 2HADNT and 4HADNT. The purity of each HADNT was approximately 98%, based on the results of high-performance liquid chromatographic analyses. 2HADNT and 4HADNT are identified by obtaining their mass spectra with laser time-of-flight MS. 2HADNT and 4HADNT dissolve in distilled water and are spontaneously broken down with time. Also, heat treatment (increasing temperatures) and dissolved oxygen accelerate the destruction of HADNTs. This technique may be applicable for the identification and exact quantitative analysis of unstable and fragile compounds such as HADNTs.