Enzymes in the mitochondrial respiratory chain are involved in various physiological events in addition to their essential role in the production of ATP by oxidative phosphorylation. The use of specific and potent inhibitors of complex I (NADH-ubiquinone reductase) and complex III (ubiquinol-cytochrome c reductase), such as rotenone and antimycin, respectively, has allowed determination of the role of these enzymes in physiological processes. However, unlike complexes I, III, and IV (cytochrome c oxidase), there are few potent and specific inhibitors of complex II (succinate-ubiquinone reductase) that have been described. In this article, we report that atpenins potently and specifically inhibit the succinate-ubiquinone reductase activity of mitochondrial complex II. Therefore, atpenins may be useful tools for clarifying the biochemical and structural properties of complex II, as well as for determining its physiological roles in mammalian tissues. T he use of specific and potent inhibitors of respiration has enabled the investigation of how the respiratory enzymes function in physiological processes. However, unlike other enzyme complexes in the respiratory chain, there has been a lack of potent and specific inhibitors of complex II [succinateubiquinone reductase (SQR)]. Although carboxin (5,6-dihydro-2-methyl-N-phenyl-1,4-oxathiin-3-carboxamide), TTFA [4,4,4-trifluoro-1-(2-thienyl)-1,3-butanedione], and HQNO (2-heptyl-4-hydroxyquinoline N-oxide) have long been known as complex II inhibitors and have been used extensively to elucidate the structure-function relationships of complex II, rather higher concentration is required for the inhibition (1). This result has hampered the study of the structure-function relationship of the complex II enzyme, as well as its roles in physiological processes.Complex II catalyzes the oxidation of succinate in the inner membrane of mitochondria and in the cytoplasmic membrane of bacteria (1-3). In addition to its function as a dehydrogenase in the respiratory system, complex II plays an important role in the tricarboxylic acid cycle. Mitochondrial complex II is an integral membrane protein consisting of four subunits (Fig. 1). The largest subunit is the 70-kDa, FAD-containing flavoprotein subunit (Fp). The dehydrogenase catalytic portion of complex II is formed by Fp and an Ϸ30-kDa iron-sulfur protein subunit (Ip) containing three different types of iron-sulfur clusters. The small hydrophobic subunits, SDHC or CybL (Ϸ15 kDa) and SDHD or CybS (Ϸ13 kDa), anchor the catalytic portion to the membrane and are also required for electron transfer to quinones. In contrast to mitochondrial complex IIs, some bacterial complex IIs contain only one larger hydrophobic polypeptide as a membrane anchor (see ref. 4 for reviews).In addition to its essential role in energy production, various recent findings suggest that mutant variants of complex II are involved in causing diverse physiological disorders. For instance, a mutation in the CybL subunit in Caenorhabditis elegans (mev-1 mutant) resu...

Six phenolic antioxidative compounds [5-caffeoylquinic acid (chlorogenic acid), 3,5-dicaffeoylquinic acid, quercetin 3-galactoside, quercetin 3-glucoside, quercetin 3-(6-malonylglucoside), and quercetin 3-(6-malonylgalactoside) (tentative)] were identified from the leaves of Corchorus olitorius L. (moroheiya) by NMR and FAB-MS. The contents of these phenolic compounds, ascorbic acid, and alpha-tocopherol in C. olitorius leaves were determined, and their antioxidative activities were measured using the radical generator-initiated peroxidation of linoleic acid. The results obtained showed that 5-caffeoylquinic acid was a predominant phenolic antioxidant in C. olitorius leaves.

Conspectus Photocatalytic and photoelectrochemical CO2 reduction of artificial photosynthesis is a promising chemical process to solve resource, energy, and environmental problems. An advantage of artificial photosynthesis is that solar energy is converted to chemical products using abundant water as electron and proton sources. It can be operated under ambient temperature and pressure. Especially, photocatalytic CO2 reduction employing a powdered material would be a low-cost and scalable system for practical use because of simplicity of the total system and simple mass-production of a photocatalyst material. In this Account, single particulate photocatalysts, Z-scheme photocatalysts, and photoelectrodes are introduced for artificial photosynthetic CO2 reduction. It is indispensable to use water as an electron donor (i.e., reasonable O2 evolution) but not to use a sacrificial reagent of a strong electron donor, for achievement of the artificial photosynthetic CO2 reduction accompanied by ΔG > 0. Confirmations of O2 evolution, a ratio of reacted e– to h+ estimated from obtained products, a turnover number, and a carbon source of a CO2 reduction product are discussed as the key points for evaluation of photocatalytic and photoelectrochemical CO2 reduction. Various metal oxide photocatalysts with wide band gaps have been developed for water splitting under UV light irradiation. However, these bare metal oxide photocatalysts without a cocatalyst do not show high photocatalytic CO2 reduction activity in an aqueous solution. The issue comes from lack of a reaction site for CO2 reduction and competitive reaction between water and CO2 reduction. This raises a key issue to find a cocatalyst and optimize reaction conditions defining this research field. Loading a Ag cocatalyst as a CO2 reduction site and NaHCO3 addition for a smooth supply of hydrated CO2 molecules as reactant are beneficial for efficient photocatalytic CO2 reduction. Ag/BaLa4Ti4O15 and Ag/NaTaO3:Ba reduce CO2 to CO as a main reduction reaction using water as an electron donor even in just water and an aqueous NaHCO3 solution. A Rh–Ru cocatalyst on NaTaO3:Sr gives CH4 with 10% selectivity (Faradaic efficiency) based on the number of reacted electrons in the photocatalytic CO2 reduction accompanied by O2 evolution by water oxidation. Visible-light-responsive photocatalyst systems are indispensable for efficient sunlight utilization. Z-scheme systems using CuGaS2, (CuGa)1–x Zn2x S2, CuGa1–x In x S2, and SrTiO3:Rh as CO2-reducing photocatalyst, BiVO4 as O2-evolving photocatalyst, and reduced graphene oxide (RGO) and Co-complex as electron mediator or without an electron mediator are active for CO2 reduction using water as an electron donor under visible light irradiation. These metal sulfide photocatalysts have the potential to take part in Z-scheme systems for artificial photosynthetic CO2 reduction, even though their ability to extract electrons from water is insufficient. A photoelectrochemical system using a photocathode is also attractive for CO2 reducti...

Glycosides are known to be precursors of the alcoholic aroma compounds of black tea. They are hydrolyzed by endogenous glycosidases during the manufacturing process. Changes in the amounts of these glycosides during the manufacturing process were investigated by using a capillary gas chromatographic--mass spectrometric analysis after trifluoroacetyl derivatization of the tea glycosidic fractions. Primeverosides were 3-fold more abundant than glucosides in fresh leaves, but they decreased greatly during the manufacturing process, especially during the stage of rolling. After the final stage of fermentation, primeverosides had almost disappeared, whereas glucosides were substantially unchanged. These results show that hydrolysis of the glycosides mainly occurred during the stage of rolling and confirm that primeverosides are the main black tea aroma precursors. This was also supported by the changes in the glycosidase activities in tea leaves. The glycosidase activities remained at a high level during withering but decreased drastically after rolling.

Optimization of the solid-phase extraction cleanup procedure enabled the GC-MS analysis of acrylamide in tea samples without the interference of bromination by tea catechins. Although polyvinylpolypyrrolidone (PVPP) is available for removing tea catechins from tea extract, the peaks derived from PVPP had the same retention time as brominated acrylamide in mass chromatograms obtained by GC-MS. A considerable amount of acrylamide was formed at roasting temperatures of > or =120 degrees C; the highest acrylamide level was observed when tea samples were roasted at 180 degrees C for 10 min. Higher temperatures and longer processing times caused a decrease in the acrylamide content. Furthermore, an analysis of 82 tea samples showed that rather than the reducing sugar content, the asparagine content in tea leaves was a significant factor related to acrylamide formation in roasted products. The acrylamide level in roasted tea products was controlled by asparagine in the presence of reducing sugars.

A Z-scheme of a linear conjugated polymer photocatalyst and a metal oxide is able to facilitate overall water splitting without non-scalable sacrificial reagents showing potential for sustainable hydrogen production.

We demonstrated photocatalytic CO2 reduction using water as an electron donor under visible light irradiation by a Z-scheme photocatalyst and a photoelectrochemical cell using bare (CuGa)0.5ZnS2 prepared by a flux method as a CO2-reducing photocatalyst. The Z-scheme system employing the bare (CuGa)0.5ZnS2 photocatalyst and RGO-(CoO x /BiVO4) as an O2-evolving photocatalyst produced CO of a CO2 reduction product accompanied by H2 and O2 in a simple suspension system without any additives under visible light irradiation and 1 atm of CO2. When a basic salt (i.e., NaHCO3, NaOH, etc.) was added into the reactant solution (H2O + CO2), the CO formation rate and the CO selectivity increased. The same effect of the basic salt was observed for sacrificial CO2 reduction using SO3 2– as an electron donor over the bare (CuGa)0.5ZnS2 photocatalyst. The selectivity for the CO formation of the Z-schematic CO2 reduction reached 10–20% in the presence of the basic salt even in an aqueous solution and without loading any cocatalysts on the (CuGa)0.5ZnS2 metal sulfide photocatalyst. It is notable that CO was obtained accompanied by reasonable O2 evolution, indicating that water was an electron donor for the CO2 reduction. Moreover, the present Z-scheme system also showed activity for solar CO2 reduction using water as an electron donor. The bare (CuGa)0.5ZnS2 powder loaded on an FTO glass was also used as a photocathode for CO2 reduction under visible light irradiation. CO and H2 were obtained on the photocathode with 20% and 80% Faradaic efficiencies at 0.1 V vs RHE, respectively.

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