The Expression Pattern of NAD(P)H Oxidases and the Cyclic Electron Transport Pathway around Photosystem I of Synechocystis sp. PCC6803 Depend on Growth Conditions

Cyclic electron transport and NADH and/or NADPH (NAD(P)H)-oxidizing activities were investigated in Synechocystis sp. PCC6803 grown under various stressed conditions and in ndhB-less (M55) and ycf33-deletion mutants. Activity staining and inhibitor data suggested that the ferredoxin-quinone reductase (FQR) route is the main pathway in ycf33-deletion and high-light (300 μE m^?2 s^?1)-grown cells as well as in M55 cells. The FQR route was highly sensitive to HgCl₂, but not to diphenyleneiodonium (DPI). On the other hand, cells grown under low CO₂ (0.03%) or normal (100 μE m^?2 s^?1, 3% CO₂) conditions were found perhaps to use the complex I-type NAD(P)H dehydrogenase route, which was found to be highly sensitive to DPI but not to HgCl₂. In high-salt (0.55 M NaCl)-grown cells, the amount of ferredoxin-NADP⁺ oxidoreductase (FNR) increased, and the main cyclic electron flow was perhaps the FNR route. Both DPI and HgCl₂ were strong inhibitors of the FNR route.     

Seasonal cycle in vitamin A1/A2-based visual pigment composition during the life history of coho salmon (Oncorhynchus kisutch)

Microspectrophotometry of rod photoreceptors was used to follow variations in visual pigment vitamin A₁/A₂ ratio at various life history stages in coho salmon. Coho parr shifted their A₁/A₂ ratio seasonally with A₂ increasing during winter and decreasing in summer. The cyclical pattern was statistically examined by a least-squares cosine model, fit to the 12-month data sets collected from different populations. A₁/A₂ ratio varied with temperature and day length. In 1+ (>12 month old) parr the A₂ to A₁ shift in spring coincided with smoltification, a metamorphic transition preceding seaward migration in salmonids. The coincidence of the shift from A₂ to A₁ with both the spring increase in temperature and day length, and with the timing of seaward migration presented a challenge for interpretation. Our data show a shift in A₁/A₂ ratio correlated with season, in both 0+ (<12 months old) coho parr that remained in fresh water for another year and in oceanic juvenile coho. These findings support the hypothesis that the A₁/A₂ pigment pair system in coho is an adaptation to seasonal variations in environmental variables rather than to a change associated with migration or metamorphosis.     

GROWTH,PHOTOSYNTHESIS AND MAINTENANCE METABOLIC COST IN THE DIATOM PHAEODACTYLUM TRICORNUTUM AT VERY LOW LIGHT LEVELS 1

The compensation point for growth of Phaeodactylum tricornutum Bohlin is less than 1 μmol. m^?2s^?1. Growth at low PFDs (<3.5 μmol. m^?2.s^?1) does not appear to reduce the maximum quantum efficiency of photosynthesis (ø_m) or to greatly inhibit the potential for light-saturated, carbon-specific photosynthesis (P_m^c). The value for ø_m in P. tricornutum is 0.10–0.12 mol O₂-mol photon^?1, independent of acclimation PFD between 0.75 and 200 μmol.m^?2.s^?1 in nutrient-sufficient cultures. P_m^c in cells of P. tricornutum acclimated to PFDs <3.5 μmol m^?2?s^?1 is approximately 50% of the highest value obtained in nutrient-sufficient cultures acclimated to growth-rate-saturating PFDs. In addition, growth at low PFDs does not severely restrict the ability of cells to respond to an increase in light level. Cultures acclimated to growth at lees than 1% of the light-saturated growth rate respond rapidly to a shift-up in PFD after a short initial lag period and achieve exponential growth rates of 1.0 d^?1 (65% of the light- and nutrient-saturated maximum growth rate) at both 40 and 200 μmol.m^?2.s^?1     

Synthesis of new organotitanium (IV) complexes Cp2Ti(SeR)2 and Cp2TiCl(SeR) via tandem reactions involving `Cp2Ti' intermediate. Crystal structures of Cp2TiCl(SeR) (R=p-ClC6H4, p-BrC6H4)

A simple and convenient route for synthesizing organotitanium (IV) complexes with a general formula Cp₂Ti(SeR)₂ or Cp₂TiCl(SeR) has been developed. This synthetic route includes reduction of Cp₂TiCl₂ with Mg and an in situ treatment of the intermediate `Cp₂Ti' with diselenides RSeSeR. Interestingly, while the route involving reaction of Cp₂TiCl₂, Mg and RSeSeR in a molar ratio of 1:1:1 produced Cp₂Ti(SeR)₂, (1-5, R=α-C₁₀H₇, o-MeC₆H₄, m-MeC₆H₄, p-ClC₆H₄, p-BrC₆H₄) in 91-97% yields, the route involving reaction of Cp₂TiCl₂, Mg and RSeSeR in a molar ratio of 1: 0.5: 0.5 afforded Cp₂TiCl(SeR) (6-7, R=p-ClC₆H₄, p-BrC₆H₄) in 70% and 92% yields, respectively. 1-7 are new and have been characterized by elemental analysis and spectroscopy, as well as by X-ray diffraction analysis for 6 and 7. A possible pathway for production of these two types of organotitanium (IV) complexes, mainly depending upon the molar ratio of the starting materials, are briefly discussed.     

In situ absorption of aflatoxins in rat small intestine

To evaluate the rate at which the four main aflatoxins (aflatoxins B₁, B₂, G₁ and G₂) are able to cross the luminal membrane of the rat small intestine, a study about intestinal absorption kinetics of these mycotoxins has been made. In situ results obtained showed that the absorption of aflatoxins in rat small intestine is a very fast process that follows first-order kinetics, with an absorption rate constant (k _a ) of 5.84±0.05 (aflatoxin B₁), 4.06±0.09 (aflatoxin B₂), 2.09±0.03 (aflatoxin G₁) and 1.58±0.04 (aflatoxin G₂) h^–1, respectively.     

Low‐Temperature Reduction Strategy Synthesized Si/Ti3C2 MXene Composite Anodes for High‐Performance Li‐Ion Batteries

Silicon is attracting enormous attention due to its theoretical capacity of 4200 mAh g^?1 as an anode for Li‐ion batteries (LIBs). It is of fundamental importance and challenge to develop low‐temperature reaction route to controllably synthesize Si/Ti₃C₂ MXene LIBs anodes. Herein, a novel and efficient strategy integrating in situ orthosilicate hydrolysis and a low‐temperature reduction process to synthesize Si/Ti₃C₂ MXene composites is reported. The hydrolysis of tetraethyl orthosilicate leads to homogenous nucleation and growth of SiO₂ nanoparticles on the surface of Ti₃C₂ MXene. Subsequently, SiO₂ nanoparticles are reduced to Si via a low‐temperature (200 °C) reduction route. Importantly, Ti₃C₂ MXene not only provides fast transfer channels for Li⁺ and electrons, but also relieves volume expansion of Si during cycling. Moreover, the characteristics of excellent pseudocapacitive performance and high conductivity of Ti₃C₂ MXene can synergistically contribute to the enhancement of energy storage performance. As expected, Ti₃C₂/Si anode exhibits an outstanding specific capacity of 1849 mAh g^?1 at 100 mA g^?1, even retaining 956 mAh g^?1 at 1 A g^?1. The low‐temperature synthetic route to Si/Ti₃C₂ MXene electrodes and involved battery‐capacitive dual‐model energy storage mechanism has potential in the design of novel high‐performance electrodes for energy storage devices.     

Initial Steps in the Pathway for Bacterial Degradation of Two Tetrameric Lignin Model Compounds

We investigated the metabolic route by which a lignin tetramer-degrading mixed bacterial culture degraded two tetrameric lignin model compounds containing β—O—4 and 5—5 biphenyl structures. The α-hydroxyl groups in the propane chain of both phenolic and nonphenolic tetramers were first oxidized symmetrically in two successive steps to give monoketones and diketones. These ketone metabolites were decomposed through C_α(=O)—C_β cleavage, forming trimeric carboxyl acids which were further metabolized through another C_α(=O)—C_β cleavage. Dehydrodiveratric acid, which resulted from the cleavage of the carbon bonds of the nonphenol tetramer, was demethylated twice. Four metabolites of the phenolic tetramer were purified and identified. All of these were stable compounds in sterile mineral medium, but were readily degraded by lignin tetramer-degrading bacteria along the same pathway as the phenol tetramer. No monoaromatic metabolites accumulated. All metabolites were identified by mass and proton magnetic resonance spectrometry. The metabolic route by which the mixed bacterial culture degraded tetrameric lignin model compounds was different from the route of the main ligninase-catalyzed C_α—C_β cleavage by Phanerochaete chrysosporium.     

Synthesis of diastereomeric bis-unsaturated prostaglandins

With the report given herein all diastereomers of PGF₂, PGE₂, and PGD₂ which bear the naturally recognized 15-S hydroxylated center, whether in the natural or $\text{ent}$-prostanoic acid skeleton, have been prepared by a route involving initial introduction of the carboxyl (α) chain (1). A major advantage of the initial α-ylation⁺ route is the facile reduction of the 13,14-en-15-one system with methanolic NaBH₄ which proceeds without competing 1,4-reduction. The products are thus free of 13,14-dihydro-PG₂ contaminants (2). The initial pharmaco logical evaluation of these diastereomers will be submitted for publication in this journal (3).     

Syntheses, structural characterizations and electronic absorption spectra simulation of three phenylimido substituted hexamolybdates incorporating a remote chloro group

Three monofunctionalized organoimido derivatives of [Mo₆O₁₉]²⁻ bearing an electron-withdrawing chloro group (R = p-ClC₆H₄1, m-ClC₆H₄2, or o-ClC₆H₄3) have been prepared in high purity and moderate to good yields using an easy reaction route of [α-Mo₈O₂₆]⁴⁻ with corresponding aromatic amine hydrochlorides or a mixture of aromatic amines and their hydrochloride salts in the presence of N,N′-dicyclohexylcarbodiimide (DCC). These complexes have been characterized by ¹H NMR, IR, UV-Vis, UV-Vis-NIR reflectance spectroscopy, cyclic voltammetry, and their semiconductive and redox properties were explored by these techniques. Their electronic absorption spectra were also interpreted based on first-principles electronic structure calculations and these features of the simulated spectra are qualitatively consistent with the observed UV spectra. Additionally, the composition and structure of compounds 1 and 2 were further confirmed by X-ray single-crystal diffraction studies.     

EFFICIENT CHEMO-ENZYMATIC SYNTHESES OF PHARMACEUTICALLY USEFUL UNNATURAL 2′-DEOXYNUCLEOSIDES

Our chemo-enzymatic method was successfully applied to the synthesis of 2-chloro-2′-deoxyadenosine (CdA, cladribine) in two ways: 1) direct conversion of chemically synthesized 2-deoxy-α-D-ribose 1-phosphate (dRP) to CdA; 2) a two-step route via 9-(2-deoxy-β-D-ribos-1-yl)-2,6-dichloropurine (Cl₂Pu-dR, 5).     

Manganese transport by caco-2 cells

The uptake and transport kinetics of manganese (Mn) were investigated in the human intestinal Caco-2 cell line both from the absorption side (apical to basolateral) and from the exsorption side (basolateral to apical). With regard to the former, transport versus time revealed (as uptake) a biphasic pattern with an initial transient phase followed by steady-state conditions. Uptake versus Mn concentrations showed saturation-type kinetics with a 100% increase of Mn binding capacity when measurements were made from 0.5 to 2 h of incubation. The transport characteristics in steady-state conditions exhibited two components, saturable (V_max = 3.70 ± 0.07 nmol/cm²/h, K_m = 32.2 ± 3.4 μM) and nonsaturable (slope = [1.4 ± 0.2] x 10^-6 cm^-2/h) usually presumed to reflect transcellular (carrier mediated) and paracellular (diffusional) pathways, respectively. Mn fluxes were decreased by calcium and calcium antagonists, almost 100% inhibited at 4°C, and affected by quinacrine and ouabain. The inhibition of ATP synthesis was apparently ineffective. From the exsorption side, the Mn fluxes, without a transient period, had an approx 20-fold smaller rate than in the absorptive direction and showed mainly a nonsaturable route (slope = [0.6 ± 0.1] x 10^-6 cm^-2/h). The mechanisms participating in the Mn movements through the monolayer are discussed and proposed to be in common, at least partly, with other divalent cations such as calcium, zinc, or iron.     

Iron and cadmium uptake by duodenum of hypotransferrinaemic mice

Absorption from food is an important route for entry of the toxic metal, cadmium, into the body. Both cadmium and iron are believed to be taken up by duodenal enterocytes via the iron regulated, proton-coupled transporter, DMT1. This means that cadmium uptake could be enhanced in conditions where iron absorption is increased. We measured pH dependent uptake of ¹⁰⁹Cd and ⁵⁹Fe by duodenum from mice with an in vitro method. Mice with experimental (hypoxia, iron deficiency) or hereditary (hypotransferrinaemia) increased iron absorption were studied. All three groups of mice showed increased ⁵⁹Fe uptake (p<0.05) compared to their respective controls. Hypotransferrinaemic and iron deficient mice exhibited an increase in ¹⁰⁹Cd uptake (p<0.05). Cadmium uptake was not, however, increased by lowering the medium pH from 7.4 to 6. In contrast, ⁵⁹Fe uptake (from ⁵⁹FeNTA₂) and ferric reductase activity was increased by lowering medium pH in control and iron deficient mice (p<0.05). The data show that duodenal cadmium uptake can be increased by hereditary iron overload conditions. The uptake is not, however, altered by lowering medium pH suggesting that DMT1-independent uptake pathways may operate.     

Electron transfer between cytochrome c2 and the tetraheme cytochrome c in Rhodopseudomonas viridis

Kinetics of electron transfer from soluble cytochrome c₂ to the tetraheme cytochrome c have been measured in isolated reaction centers and in membrane fragments of the photosynthetic purple bacterium Rhodopseudomonas viridis by time-resolved flash absorption spectroscopy. Absorbance changes kinetics in the region of cytochrome -bands (540–560 nm) were measured at 21 °C under redox conditions where the two high-potential hemes (c-559 and c-556) of the tetraheme cytochrome were chemically reduced. After flash excitation, the heme c-559 donates an electron to the special pair of bacteriochlorophylls and is then re-reduced by heme c-556. The data show that oxidized heme c-556 is subsequently re-reduced by electron transfer from reduced cytochrome c₂ present in the solution. The rate of this reaction has a non-linear dependence on the concentration of cytochrome c₂, suggesting a (minimal) two-step mechanism involving the f ormation of a complex between cytochrome c₂ and the reaction center, followed by intracomplex electron transfer. To explain the monophasic character of the reaction kinetics, we propose a collisional mechanism where the lifetime of the temporary complex is short compared to electron transfer. The limit of the halftime of the bimolecular process when extrapolated to high concentrations of cytochrome c₂ is 60 ± 20 s. There is a large ionic strength effect on the kinetics of electron transfer from cytochrome c₂ to heme c-556. The pseudofirst-order rate constant decreases from 1.1 × 10⁷ M^-1 s^-1 to 1.3 × 10⁶ M^-1 s^-1 when the ionic strength is increased from 1 to 1000 mM. The maximum rate (1.1 × 10⁷ M^-1 s^-1) was obtained at about 1 mM ionic strength. This dependence of the rate on ionic strength s uggests that attractive electrostatic interactions contribute to the binding of cytochrome c₂ with the tetraheme cytochrome. On the basis of our data and of previous molecular modelling, it is proposed that cytochrome c₂ docks close to the low-potential heme c-554 and reduces heme c-556 via c-554.     

Dietary and metabolite effects on trivalent chromium retention and distribution in rats

The purpose of this study was to determine if diet or various metabolites alter chromium (Cr) uptake and distribution in rats. Radioactively labeled Cr was detected within 15 min of oral administration to rats, and the total amount retained remained relatively constant from 1 to 24 h. Dietary Cr intake did not alter Cr retention or distribution. The majority of the Cr was retained in the carcass. However, when the amount of labeled Cr was expressed per gram of tissue, the highest amounts of Cr were found in the kidneys, spleen, and pancreas. Pharmacological doses of insulin, epinephrine, glucagon, and dibutyryladenosine-3’ −5’ cyclic monophosphate, prostaglandins A₁, A₂, B₁, B₂, E₁, E₂, F_1α, and F_2α did not significantly influence Cr retention. Glucose, sucrose, nicotinic acid, glutathione, and other metabolites administered orally in conjunction with labeled Cr also did not significantly alter Cr retention. These data indicate that most nutrients and metabolites do not alter Cr retention and distribution. The regulation of Cr homeostasis appears to be at the level of excretion.     

Synthetic Studies on Cyclopentane Derivatives

An alternative route to dl-prostaglandin-B₁ using the Grignard reaction of 2-(6′-tert-butyloxycarbonylhexyl)-3-methoxy-2-cyclopenten-1-one(XII) with 3-tetrahydropyranyloxy-1-octyne was developed.

An easy synthesis of dihydrojasmone was also described.     

Enhanced Electrocatalysis for Hydrogen Evolution Reactions from WS2 Nanoribbons

A facile route is developed to boost the electrocatalytic activity of WS₂ by chemically unzipping WS₂ nanotubes to form WS₂ nanoribbons (NRs) with increased edge content. Analysis indicates that the hydrogen evolution reaction activity is strongly associated with the number of exposed active edge sites. The formation of WS₂ NRs is an effective route for controlling the electrochemical properties of the 2D dichalcogenides, enabling their application in electrocatalysis.     

Synthesis,characterization, and evaluation of novel cell‐penetrating peptides based on TD‐34

In this study, six N‐1, N‐2, or N‐11 derivatives of TD‐34 (a cationic cyclic cell‐penetrating peptide [CPP], ACSSKKSKHCG) were designed and synthesized including both linear peptides and cyclic peptides, such as DL‐1 (KWSSKKSKHCG), DLCC‐1 (cyclopeptide, KWSSKKSKHCG), DL‐2 (KWSSKKSKHCG‐NH₂), DLCC‐2 (cyclopeptide, KWSSKKSKHCG‐NH₂), DL‐3 (RWSSKKSKHCG), and DLCC‐3 (cyclopeptide, RWSSKKSKHCG). The cyclic peptides were synthesized by disulfide bound linkages formed by N‐2 and N‐10 cysteine. In vitro penetration experiment was conducted to investigate the transdermal enhancement ability of these derivatives, using triptolide (TP) as model drug. The results display that at the presence of DLCC‐2, the accumulative penetration amount of TP increased 1.71‐fold (P < .05) within 12 hours, displaying better transdermal enhancing ability than TD‐34. Meanwhile, DL‐3 and DLCC‐3 slightly decreased the transdermal delivery of TP, and the presence of DL‐1 and DLCC‐1 shows no obvious effect. In order to clarify the factors on the transdermal ability of peptides, the solubility of TP in phosphate buffer saline (PBS) at the presence of different peptides and the mechanism of transdermal delivery of CPPs was investigated. The result shows that most of these peptides have no significant effect on the solubility of TP except DLCC‐3 (the solubility of TP slightly increased). And in order to investigate transdermal absorption route of DLCC‐2, polyarginine linked to rhodamine b (Rh b) derivative is used. The result proved that the transdermal route of polyarginine is via hair follicle, which may change the transdermal route of its cargo molecule (TP). Our group previously proved that polyarginine and TD‐34 have similar transdermal enhancing mechanism (changing the transdermal route of their cargo molecule); it is reasonably speculated that the transdermal route of DLCC‐2 is the same as polyarginine and then changes the transdermal absorption route of TP. Furthermore, such results have laid a solid foundation for further investigation of CPPs and paved a way for both designing and synthesizing of new drug delivery system for therapy molecules.     

Effect of HCO - 3 concentration in the absorption solution on the energetic coupling of H+-cotransports in roots of Zea mays L.

The effect of HCO ₃ ^- on ion absorption by young corn roots was studied in conditions allowing the independent control of both the pH of uptake solution and the CO₂ partial pressure in air bubbled through the solution. The surface pH shift in the vicinity of the outer surface of the plasmalemma induced by active H⁺ excretion was estimated using the initial uptake rate of acetic acid as a pH probe (Sentenac and Grignon (1987) Plant Physiol. 84, 1367). Acetic acid and orthophosphate uptake rates and NO ₃ ^- accumulation were slowed down, while ⁸⁶Rb⁺ uptake and K⁺ accumulation rates were increased by HCO ₃ ^- . These effects were similar to those induced by 4-(2-hydroxyethyl)-1-piperazineethane sulfonic acid/2-amino-2-(hydroxymethyl)-1,3-propanediol (Hepes-Tris). They were more pronounced when the H⁺ excretion was strong, were rapidly reversible and were not additive to those of Hepes-Tris. The hypothesis is advanced that the buffering system CO₂/H₂CO₃/HCO ₃ ^- accelerated the diffusion of equivalent H⁺ inside the cell wall towards the medium. This attenuated the surface pH shift in the vicinity the plasma membrane and affected the coupling between the proton pump and cotransport systems.Abbreviations FW fresh weight - Hepes 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid - J_aa acetic acid influx - J_K ⁺ K⁺ influx - J_Pi orthophosphate influx - Mes 2-(N-morpholino)ethanesulfonic acid - pCO₂ CO₂ partial pressure - Tris 2-amino-2-(hydroxymethyl)-1,3-propanediol     

Definitive Solution Structures for the 6-Formylated Versions of 1-(βD-Ribofuranosyl)-, 1-(2′-Deoxy-β-D-Ribofuranosyl)-, and 1-β-D-Arabinofuranosyluracil,and of Thymidine

Abstract

ROESY and NOESY NMR spectroscopic analyses of the ribofuranosyl (1a), 2′-deoxyribofuranosyl (1b), and arabinofuranosyl (1c) derivatives of 6-formyluracil in (CD₃)₂SO and D₂O solutions have established that each exclusive 7,05′-cyclic hemiacetal diastereomer of 1a,b and the major 7,O2′-cyclic hemiacetal diastereomer of 1c possess the 7R configuration. In addition, (7R)-1c has been shown to be thermodynamically more stable than (7S)-1c, contrary to our previous indication. A new, higher yielding synthetic route to 1a has been developed, 1b has been obtained for the first time in crystalline form, the route to 1c has been modified to better accommodate large scale preparations, and a new, fourth member of this class, 6-formylthymidine (1d), has been synthesized and its solution structures in (CD₃)₂SO, D₂O, and CD₃OD have been determined. Antitumor and antiviral evaluations of 1a-c have revealed no significant levels of activity.     

Interplay between glutathione, Atx1 and copper: X-ray absorption spectroscopy determination of Cu(I) environment in an Atx1 dimer

X-ray absorption techniques have been used to characterise the primary coordination sphere of Cu(I) bound to glutathionate (GS⁻), to Atx1 and in Cu₂^I(GS⁻)₂(Atx1)₂, a complex recently proposed as the major form of Atx1 in the cytosol. In each complex, Cu(I) was shown to be triply coordinated. When only glutathione is provided, each Cu(I) is triply coordinated by sulphur atoms in the binuclear complex Cu^I ₂(GS⁻)₅, involving bridging and terminal thiolates. In the presence of Atx1 and excess of glutathione, under conditions where Cu^I ₂(GS⁻)₂(Atx1)₂ is formed, each Cu(I) is triply coordinated by sulphur atoms. Given these constraints, there are two different ways for Cu(I) to bridge the Atx1 dimer: either both Cu(I) ions contribute to bridging the dimer, or only one Cu(I) ion is responsible for bridging, the other one being coordinated to two glutathione molecules. These two models are discussed as regards Cu(I) transfer to Ccc2a.