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.
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