Senescence in the aging process.

The accumulation of 'senescent' cells has long been proposed to act as an ageing mechanism. These cells display a radically altered transcriptome and degenerative phenotype compared with their growing counterparts. Tremendous progress has been made in recent years both in understanding the molecular mechanisms controlling entry into the senescent state and in the direct demonstration that senescent cells act as causal agents of mammalian ageing. The challenges now are to gain a better understanding of how the senescent cell phenotype varies between different individuals and tissues, discover how senescence predisposes to organismal frailty, and develop mechanisms by which the deleterious effects of senescent cells can be ameliorated

Lithium ion sensors

The detection and monitoring of lithium in environmental and clinical settings is becoming increasingly important. In this review, sensors incorporating conductive polymers and lithium bronzes are discussed, together with electrochemical and spectroscopic approaches. Ionophore-based methods have been employed extensively, with varying degrees of selectivity and sensitivity, and these are discussed in depth

The conducting structure and voltammetric behaviour of graphite-epoxy resin composite electrodes for on-line chlorine sensing

EThOS - Electronic Theses Online ServiceGBUnited Kingdo

The conducting structure and voltammetric behaviour of graphite-epoxy resin composite electrodes for on-line chlorine sensing

EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Biosynthesis of bacteriochlorophylls in purple bacteria

The purple bacteria make bacteriochlorophylls for the photosynthetic mode of growth. These pigments are made from the simple precursors glycine and succinyl CoA and the initial steps in the pathway of bacteriochlorophyll biosynthesis are shared with the vitamin B12 and heme biosynthetic pathways. This chapter concentrates on the biochemical properties of the enzymes involved in each step of the pathway and the discovery and assignment of the genes encoding these enzymes. The characterization of purple bacterial enzymes involved in these steps has been crucial in understanding similar enzymes from other sources. The characterization of the early steps in the pathway within purple bacteria, such as δ-aminolevulinate synthase, contributed significantly to the understanding of the mammalian enzymes in the 1950s and 1960s. More recently the study of the purple bacterial enzymes toward the end of the pathway has been instrumental in identifying and characterizing the orthologous enzymes from cyanobacteria and plants. In this review we present the details of the properties of these enzymes from the purple bacteria, such as purification methods and kinetic analyses from the early literature, through to more recent studies using recombinant purple bacterial enzymes.23 page(s

On the microelectrode behaviour of graphite-epoxy composite electrodes

Electrodes fashioned from conducting particles embedded in insulating binder show some properties commonly associated with arrays of microelectrodes, viz. independence of current from convective flow and sigmoidal current–voltage curves. We have systematically investigated the electrochemical behaviour of a range of composite formulations. The fraction of the surface area that is conducting and the size of the conducting features have been quantified using the novel technique of conducting atomic force microscopy (C-AFM). We have shown that flow sensitivity and voltammetric behaviour are correlated with results from the C-AFM. The more dilute formulations behave like arrays of microelectrodes, though exhibiting large time constants. The origin of this behaviour is discussed. Keywords: Composite electrodes, Microelectrodes, Conducting atomic force microscop

Phytobilin biosynthesis: the Synechocystis sp PCC 6803 heme oxygenase-encoding ho1 gene complements a phytochrome-deficient Arabidopsis thaliana hy1 mutant

The phytobilin chromophores of phycobiliproteins and phytochromes are biosynthesized from heme in a pathway that begins with the opening of the tetrapyrrole macrocycle of protoheme to form biliverdin Ixα, in a reaction catalyzed by heme oxygenase. An Arabidopsis thaliana hy1 mutant was previously shown to be deficient in phytochrome responses, and these responses were regained when the plants were administered biliverdin Ixα. A heme oxygenase-encoding gene, ho1, was recently cloned from the cyanobacterium Synechocystis sp. Pcc 6803. When ho1 was expressed in Escherichia coli, the cells produced active ferredoxin-dependent soluble heme oxygenase. The open reading frame of ho1 was fused in frame with a chloroplast transit peptide-encoding sequence from the oli gene of Antirrhinum majus. This construct was placed in a binary plasmid vector containing a kanamycin resistance marker and a cauliflower mosaic virus 35s promoter to control expression of the chimeric oli-ho1 gene and used to transform A. thaliana hy1 plants. Two independent transformed lines were obtained that had the phenotype of the parental Landsberg erecta line and expressed the chimeric gene, as indicated by detection of its mRNA by reverse transcriptase-polymerase chain reaction. The results indicate that Synechocystis sp. PCC 6803 heme oxygenase encoded by ho1 can substitute for the defective HY1 gene product and that the only required enzyme activity of the HY1 gene product is heme oxygenase.8 page(s

Strategic Distribution of Protective Proteins within Bran Layers of Wheat Protects the Nutrient-Rich Endosperm1[C][W][OA]

Bran from bread wheat (Triticum aestivum ‘Babbler’) grain is composed of many outer layers of dead maternal tissues that overlie living aleurone cells. The dead cell layers function as a barrier resistant to degradation, whereas the aleurone layer is involved in mobilizing organic substrates in the endosperm during germination. We microdissected three defined bran fractions, outer layers (epidermis and hypodermis), intermediate fraction (cross cells, tube cells, testa, and nucellar tissue), and inner layer (aleurone cells), and used proteomics to identify their individual protein complements. All proteins of the outer layers were enzymes, whose function is to provide direct protection against pathogens or improve tissue strength. The more complex proteome of the intermediate layers suggests a greater diversity of function, including the inhibition of enzymes secreted by pathogens. The inner layer contains proteins involved in metabolism, as would be expected from live aleurone cells, but this layer also includes defense enzymes and inhibitors as well as 7S globulin (specific to this layer). Using immunofluorescence microscopy, oxalate oxidase was localized predominantly to the outer layers, xylanase inhibitor protein I to the xylan-rich nucellar layer of the intermediate fraction and pathogenesis-related protein 4 mainly to the aleurone. Activities of the water-extractable enzymes oxalate oxidase, peroxidase, and polyphenol oxidase were highest in the outer layers, whereas chitinase activity was found only in assays of whole grains. We conclude that the differential protein complements of each bran layer in wheat provide distinct lines of defense in protecting the embryo and nutrient-rich endosperm