An overview on chlorophylls and quinones in the photosystem I-type reaction centers

Minor but key chlorophylls (Chls) and quinones in photosystem (PS) I-type reaction centers (RCs) are overviewed in regard to their molecular structures. In the PS I-type RCs, the prime-type chlorophylls, namely, bacteriochlorophyll (BChl) a′ in green sulfur bacteria, BChl g′ in heliobacteria, Chl a′ in Chl a-type PS I, and Chl d′ in Chl d-type PS I, function as the special pairs, either as homodimers, (BChl a′)₂ and (BChl g′)₂ in anoxygenic organisms, or heterodimers, Chl a/a′ and Chl d/d′ in oxygenic photosynthesis. Conversions of BChl g to Chl a and Chl a to Chl d take place spontaneously under mild condition in vitro. The primary electron acceptors, A ₀, are Chl a-derivatives even in anoxygenic PS I-type RCs. The secondary electron acceptors are naphthoquinones, whereas the side chains may have been modified after the birth of cyanobacteria, leading to succession from menaquinone to phylloquinone in oxygenic PS I.     

Inhibition of insulin-induced activation of Akt by a kinase-deficient mutant of the epsilon isozyme of protein kinase C

Akt, also known as protein kinase B, is a protein-serine/threonine kinase that is activated by growth factors in a phosphoinositide (PI) 3-kinase-dependent manner. Although Akt mediates a variety of biological activities, the mechanisms by which its activity is regulated remain unclear. The potential role of the epsilon isozyme of protein kinase C (PKC) in the activation of Akt induced by insulin has now been examined. Expression of a kinase-deficient mutant of PKCepsilon (epsilonKD), but not that of wild-type PKCepsilon or of kinase-deficient mutants of PKCalpha or PKClambda, with the use of adenovirus-mediated gene transfer inhibited the phosphorylation and activation of Akt induced by insulin in Chinese hamster ovary cells or L6 myotubes. Whereas the epsilonKD mutant did not affect insulin stimulation of PI 3-kinase activity, the phosphorylation and activation of Akt induced by a constitutively active mutant of PI 3-kinase were inhibited by epsilonKD, suggesting that epsilonKD affects insulin signaling downstream of PI 3-kinase. PDK1 (3'-phosphoinositide-dependent kinase 1) is thought to participate in Akt activation. Overexpression of PDK1 with the use of an adenovirus vector induced the phosphorylation and activation of Akt; epsilonKD inhibited, whereas wild-type PKCepsilon had no effect on, these actions of PDK1. These results suggest that epsilonKD inhibits the insulin-induced phosphorylation and activation of Akt by interfering with the ability of PDK1 to phosphorylate Akt.     

Inhibition of actin filament depolymerization by the Dictyostelium 30,000-D actin-bundling protein

We have studied the effect of the Dictyostelium discoideum 30,000-D actin-bundling protein on the assembly and disassembly of pyrenyl-labeled actin in vitro. The results indicate that the protein is a potent inhibitor of the rate of actin depolymerization. The inhibition is rapid, dose dependent, and is observed at both ends of the filament. There is little effect of 30-kD protein on the initial rate of elongation from F-actin seeds or on the spontaneous nucleation of actin polymerization. We could detect little or no effect on the critical concentration. The novel feature of these results is that the filament ends are free for assembly but are significantly impaired in disassembly with little change in the critical concentration at steady state. The effects appear to be largely independent of the cross-linking of actin filaments by the 30-kD protein. Actin cross-linking proteins may not only cross-link actin filaments, but may also differentially protect filaments in cells from disassembly and promote the formation of localized filament arrays with enhanced stability.     

Flecainide ameliorates arrhythmogenicity through NCX flux in Andersen-Tawil syndrome-iPS cell-derived cardiomyocytes

Andersen-Tawil syndrome (ATS) is a rare inherited channelopathy. The cardiac phenotype in ATS is typified by a prominent U wave and ventricular arrhythmia. An effective treatment for this disease remains to be established. We reprogrammed somatic cells from three ATS patients to generate induced pluripotent stem cells (iPSCs). Multi-electrode arrays (MEAs) were used to record extracellular electrograms of iPSC-derived cardiomyocytes, revealing strong arrhythmic events in the ATS-iPSC-derived cardiomyocytes. Ca²⁺ imaging of cells loaded with the Ca²⁺ indicator Fluo-4 enabled us to examine intracellular Ca²⁺ handling properties, and we found a significantly higher incidence of irregular Ca²⁺ release in the ATS-iPSC-derived cardiomyocytes than in control-iPSC-derived cardiomyocytes. Drug testing using ATS-iPSC-derived cardiomyocytes further revealed that antiarrhythmic agent, flecainide, but not the sodium channel blocker, pilsicainide, significantly suppressed these irregular Ca²⁺ release and arrhythmic events, suggesting that flecainide's effect in these cardiac cells was not via sodium channels blocking. A reverse-mode Na^+/Ca²⁺exchanger (NCX) inhibitor, KB-R7943, was also found to suppress the irregular Ca²⁺ release, and whole-cell voltage clamping of isolated guinea-pig cardiac ventricular myocytes confirmed that flecainide could directly affect the NCX current (I_NCX). ATS-iPSC-derived cardiomyocytes recapitulate abnormal electrophysiological phenotypes and flecainide suppresses the arrhythmic events through the modulation of I_NCX.     

Enrichment and characterization of clonogenic epithelial cells from adult rat liver and initiation of epithelial cell strains

Summary A highly efficient method is described for obtaining prolifertive epithelial cells from adult rat livers for the reproducible establishment of liver epithelial cell strains. When cells were isolated from livers of 10-to 15-wk-old male Fischer 344 rats by a collagenase-perfusion method, collected by centrifugation at 50×g for 5 min, and cultured in Williams' medium E containing fetal bovine serum and dexamethasone, colonies of epithelial cells different in size and morphology from hepatocytes were obtained. Sequential perfusion with collagenase and dispase yielded numerous epithelial cell colonies. When isolated cells were fractionated by differential centrifugation, the great majority of hepatocytes were sedimented at 50 ×g for 1 min, whereas many non-hepatocytic cells remiined in the supernatant and could be sedimented by a second centrifugation at 50×g for 5 min. Culture of the two fractions revealed that almost all the epithelial cell colonies were derived from cells in the non-hepatocytic cell fraction. The epithelial cells were cytochemically negative for γ-glutamyl transpeptidase activity, whereas an increase in the activity was detected in hepatocytes with duration in culture. Ultrastructural characteristics of hepatocytes were not found in the cells of newly established cell strains. These results suggest that adult rat liver epithelial cells propagable in culture were derived from a cell type other than the hepatocyte.     

Reject water treatment by improvement of whole cell anammox entrapment using polyvinyl alcohol/alginate gel

Reject water treatment performance was investigated by whole cell anammox sludge entrapped polyvinyl alcohol/sodium alginate gel in the stirred tank reactor (STR). The whole experiment was conducted through Phase 1 and Phase 2 in which synthetic wastewater and modified reject water were used as feeding medium, respectively. The anammox reactor demonstrated quick start-up after 22 days as well as stable and relatively high nitrogen removal rate of more than 8.0 kg-N m⁻³ day⁻¹ during the two both phases even under moderately low temperature of 25 ± 0.5°C during the last 2 months of Phase 2. The matured brownish red PVA beads had good characteristics with buoyant density of 1.10 g cm⁻³, settling velocity of 141 m h⁻¹ and diameter of 4 mm. The bacterial community was identified by 16S rDNA analysis revealing the concurrent existence of KSU-1 and new kind anammox bacterium Kumadai-I after changing influent from synthetic wastewater to reject water. It was speculated that Kumadai-I might play a role as “promotion” factor together with KSU-1 on high nitrogen removal rate. These results demonstrate the potential application of whole cell anammox entrapment by PVA/alginate gel for achieving stable and high-rate nitrogen removal from high ammonium with low C/N ratio contained wastewaters, such as reject water, digester liquor or landfill leachate.     

Hyperosmotic stress up-regulates the expression of major vault protein in SW620 human colon cancer cells

The major vault protein (MVP) is the major constituent of the vault particle, the largest ribonuclear protein complex described to date and is identical to lung resistance-related protein (LRP). Although MVP is also expressed in several normal tissues, little is known about its physiological role. MVP played a protective role against some xenobiotics and other stresses. We thus investigated the effect of osmotic stress on MVP expression by treating human colon cancer SW620 cells with sucrose or NaCl. The expression level of both MVP protein and MVP mRNA was increased by the osmostress. Sucrose or sodium chloride could also enhance MVP promoter activity. Inhibition of p38 MAPK in SW620 cells by SB203580 inhibited the expression of MVP under hyperosmotic stress. These findings suggested that osmotic stress up-regulated the MVP expression through p38 MAPK pathway. Down-regulation of MVP expression by MVP interfering RNA (RNAi) in SW620 cells increased the sensitivity of the cells to hyperosmotic stress and enhanced apoptosis. Furthermore, MVP RNAi prevented the osmotic stress-induced, time-dependent increase in phosphorylated Akt. These findings suggest that the PI3K/Akt pathway might be implicated in the cytoprotective effect of MVP.Our data demonstrate that exposure of cells to hyperosmotic stress induces MVP that might play an important role in the protection of the cells from the adverse effects of osmotic stress.     

Notes on some plant-inhabiting fungi collected from the Nansei Islands (2)

In this paper, four fungi collected in Nansei Islands are reported. One is Strasseria garciniae, which must be transferred to the genus Phyllosticta. This fungus was collected in Okinawa Main Island and Iriomote Island. The other three fungi are newly added to the Japanese fungal flora. Phyllosticta ghaesembillae on Codiaeum variegatum and Cercospora asplenii on Asplenium antiquum were collected in Yoron Island. The last one, Coniella australiensis on Eucalyptus robusta was collected in Okinawa Main Island. Their morphology and symptoms on the host plant are described, with some mycological notes.