Hydrogen sulfide (H(2)S) is a synaptic modulator as well as a neuroprotectant. Currently, pyridoxal-5'-phosphate (PLP)-dependent cystathionine beta-synthase (CBS) is thought to be the major H(2)S-producing enzyme in the brain. We recently found that brain homogenates of CBS-knockout mice, even in the absence of PLP, produce H(2)S at levels similar to those of wild-type mice, suggesting the presence of another H(2)S-producing enzyme. Here we show that 3-mercaptopyruvate sulfurtransferase (3MST) in combination with cysteine aminotransferase (CAT) produces H(2)S from cysteine. In addition, 3MST is localized to neurons, and the levels of bound sulfane sulfur, the precursor of H(2)S, are greatly increased in the cells expressing 3MST and CAT but not increased in cells expressing functionally defective mutant enzymes. These data present a new perspective on H(2)S production and storage in the brain.

Hydrogen sulfide (H2S) is recognized as a neuromodulator as well as neuroprotectant in the brain. H2S can be produced from cysteine by enzymes such as cystathionine beta-synthase. However, a mechanism for releasing H2S under physiologic conditions has not been identified. Here we show that H2S is released from bound sulfur, an intracellular store of sulfur, in neurons and astrocytes of mice and rats in the presence of physiologic concentrations of endogenous reducing substances glutathione and cysteine. The highest pH to release H2S from another sulfur store, acid-labile sulfur, which is localized mainly in mitochondria, is 5.4. Because mitochondria are not in the acidic condition, acid-labile sulfur may not be a physiologic source of H2S. Free H2S is immediately absorbed and stored as bound sulfur. Our novel method, using silver particles to measure free H2S, shows that free H2S is maintained at a low level in basal conditions. Alkalinization of the cytoplasm is required for effective release of H2S from bound sulfur, and this condition is achieved in astrocytes by the high concentrations of extracellular K+ that are normally present when nearby neurons are excited. These data present a new perspective on the regulation of H2S in the brain.

Synthesis and reactivity of iron-dinitrogen complexes have been extensively studied, because the iron atom plays an important role in the industrial and biological nitrogen fixation. As a result, iron-catalyzed reduction of molecular dinitrogen into ammonia has recently been achieved. Here we show that an iron-dinitrogen complex bearing an anionic PNP-pincer ligand works as an effective catalyst towards the catalytic nitrogen fixation, where a mixture of ammonia and hydrazine is produced. In the present reaction system, molecular dinitrogen is catalytically and directly converted into hydrazine by using transition metal-dinitrogen complexes as catalysts. Because hydrazine is considered as a key intermediate in the nitrogen fixation in nitrogenase, the findings described in this paper provide an opportunity to elucidate the reaction mechanism in nitrogenase.

A new material concept of soft crystals is proposed. Soft crystals respond to gentle stimuli such as vapor exposure and rubbing but maintain their structural order and exhibit remarkable visual changes in their shape, color, and luminescence. Various interesting examples of soft crystals are introduced in the article. By exploring the interesting formation and phase‐transition phenomena of soft crystals through interdisciplinary collaboration, new materials having both the characteristics of ordered hard crystals and those of flexible soft matter are expected.

A subazaporphyrin (SubAP), tert-butylated and crowned subphthalocyanines (tBSubPc and SubCRPc), a μ-oxo dimer of tert-butylated SubPc {(tBSubPc)2O}, a subnaphthalocyanine (SubNc), and monosubstituted type unsymmetrical phthalocyanine (Pc) and naphthalocyanine (Nc) analogues have been synthesized. In particular, unsymmetrical Pc's and Nc's have been prepared in moderate yields by the ring expansion reaction of structurally distorted SubPc's and SubNc's with isoindolediimine derivatives in dimethyl sulfoxide−chloronaphthalene (or chlorobenzenes or aromatic hydrocarbons such as toluene and xylene) mixtures. The compounds have been characterized by electronic absorption, magnetic circular dichroism (MCD), fluorescence emission, and nuclear magnetic resonance spectroscopy. Both the Soret bands and Q-bands shift to longer wavelength and gain intensity in the order SubAP, SubPc, and SubNc. Fluorescence quantum yields and lifetimes generally decrease with decreasing molecular symmetry. Circular dichroism and NMR spectroscopy have revealed that a SubPc with three 15-crown-5 ether voids having a phenyl group as an axial ligand (SubCRPc) forms inclusion complexes with 2,6-dimethyl-β-cyclodextrin in acetonitrile or water−acetonitrile mixtures, while the electronic absorption spectroscopy suggests that it is not dimerized by the addition of cations such as K+, Rb+, Ce+, i.e., cations which are effective in dimerizing Pc's with 15-crown-5 ether voids. Molecular orbital (MO) calculations within the framework of the Pariser−Parr−Pople approximation have succeeded in reproducing the optical absorption experimental data of not only the parent subazamacrocycles but also Pc derivatives with lower symmetry obtained by the ring expansion reaction. The correspondence between MO calculations and experiments suggests strongly that, in the metal-free unsymmetrical Pc's, two pyrrole hydrogen atoms are bound to the nitrogens along the short axis. Comparison of formation, bonding, and donation energies between SubPc and typical Pc, i.e., MgPc by natural bond orbital analysis, suggests that the distortion energy is not the major reason for the ring expansion reactivity of SubPc, and that the lack of donor−acceptor stabilization in B−N(pyrrole) bonds destabilizes SubPc. Band deconvolution of the electronic absorption and MCD spectra of SubPc with the same set of bands (with the same centers and width) experimentally identified that the excited state of the Q-band of SubPc is orbitally degenerate, with three degenerate transitions located in the 250−450-nm region. In particular, the transition at 359 nm corresponds to a shoulder seen on the red side of the Soret band tail. Time-resolved EPR analysis has shown that the size of the π-system of SubPc is, indeed, smaller than that of Pc's.

a b s t r a c tPolysulfide is a bound sulfur species derived from endogenous H 2 S. When mouse neuroblastoma, Neuro2A cells were exposed to tert-butyl hydroperoxide after treatment with polysulfide, a significant decline in cell toxicity was observed. Rapid uptake of polysulfides induced translocation of Nrf2 into the nucleus, resulting in acceleration of GSH synthesis and HO-1 expression. We demonstrated that polysulfide reversibly modified Keap1 to form oxidized dimers and induced the translocation of Nrf2. Moreover, polysulfide treatment accelerated Akt phosphorylation, which is a known pathway of Nrf2 phosphorylation. Thus, polysulfide may mediate the activation of Nrf2 signaling, thereby exerting protective effects against oxidative damage in Neuro2A cells.

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DNA topoisomerase I was purified to near homogeneity from a clonal line of human lymphoblastic leukemia cells, RPMI 8402, that is resistant to camptothecin, a cytotoxic alkaloid from Camptotheca acuminata, and compared with that of the parent wild-type cells. As assayed by relaxation of the supercoiled plasmid DNA and by formation of enzymelinked DNA breaks, the purified enzyme from the resistant cells was shown to be >125-fold as resistant to camptothecin as the wild-type enzyme, comparable to a cellular resistance index of about 300. Therefore, the cellular resistance appears to be due to the resistance of the enzyme. The amount of the immunoreactive enzyme protein in whole extract appeared to be reduced to less than half that of the wild-type enzyme. These results establish that DNA topoisomerase I is the cellular target of camptothecin and that DNA topoisomerase I is essential for the survival of mammalian cells.The DNA topoisomerases are enzymes that catalyze the concerted breakage and rejoining of the DNA backbone and thereby are presumed to participate in various genetic processes (1-5). The type I topoisomerases transiently cut and reseal one DNA strand so that the linking number changes by steps of one. Genetic and functional studies of the enzymes have been largely limited to prokaryotes and the lower eukaryote yeast. Viable mutants ofEscherichia coli defective in the topA gene encoding topoisomerase I were isolated (6, 7), but these proved to have mutations in DNA gyrase genes that compensated for the mutation in topA (8-10). This finding suggested an essential role for the enzyme in regulating the degree of supercoiling of DNA by counteracting the activity of the type II enzyme. In contrast, however, topoisomerase I-deficient mutants of yeast were isolated and shown to be viable, although they possessed the wild-type allele of topoisomerase II (11,12). The effect of the topoisomerase I mutation, however, was manifested by an additional mutation in topoisomerase II, implicating the complementary role of the latter (12).Topoisomerase I was previously found associated with transcriptionally active chromatin in mammalian cells (13,14). It also appears to be catalytically active on transcriptionally active genes in Drosophila polytene chromosomes (15) as well as on nucleolus-associated ribosomal genes (16-19). These experiments suggest a functional role for the enzyme in transcriptional events involving either RNA polymerase I or II.The availability of mutants and specific inhibitors of this enzyme as was the case in prokaryotes might help dissect and establish the role of this enzyme in DNA metabolism. We previously reported that heparin is a potent inhibitor of a mammalian DNA topoisomerase I (20, 21), but its broad specificity limits its usefulness for this purpose. Camptothecin (CPT) is a cytotoxic alkaloid isolated from Camptotheca acuminata (22, 23), which has a strong antitumor activity against a wide range of experimental tumors. CPT inhibits RNA and DNA synthesis and causes rapid and rev...