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At least 811 records · Page 45Linked to original sources

PubMed2001

A potentially improved approach to methylene blue virus inactivation of plasma: the Maco Pharma Maco-Tronic system.

Plasma was subjected to methylene blue (MB) photochemical virus inactivation using the Maco Pharma Maco-Tronic system which allows three units to be illuminated together, thus reducing processing time. The plasma bag system used incorporates an integral membrane plasma filter and a dry MB pill which dissolves in the plasma to give a 1-microM concentration. There is computer-controlled processing and datalogging. In an assessment of 10 pools of Group A plasma, the losses of coagulation factors, following MB/light treatment, were 23% fibrinogen, 10% FV, 26% FVIII, 11% FIX and 13% FXI. Group O, Group B and Group AB plasmas were not tested. Von Willebrand factor (vWf) multimers showed no substantial change when treated with MB, and no losses were seen for antithrombin III (ATIII), protein C and vWf:Ag. Measurements of C3a, C5a, prothrombin fragment 1+2 and FXIIa indicated that there was no activation as a result of filtration.

Antithrombin III↗

PubMed1976

Covalently linked chlorophyll a dimer: A biomimetic model of special pair chlorophyll.

The synthesis of a covalent dimer of chlorophyll a which possesses properties strikingly similar to those exhibited by P700 special pair chlorophyll in vivo is described. The covalent dimer is characterized by several spectroscopic techniques. Hydrogen bonding nucleophiles, such as water, primary alcohols, and primary thiols, are effective in generating a species from solutions of 10 muM covalent dimer in hydrophobic solvents which absorbs light near 700 nm. Formation of this in vitro special pair is a rapid, spontaneous process at room temperature. The range of nucleophiles which promote this process suggests that amino acid residues may function in a similar fashion to form P700 in chlorophyll-protein complexes. The photochemical properties of this in vitro special pair mimic those of in vivo P700 species. The 697 nm absorption of the in vitro special pair undergoes photo-bleaching rapidly in the presence of iodine that results in the production of a cation radical which exhibits an electron spin resonance signal similar to that of oxidized P700 observed in Chlorella vulgaris.

Journal Article↗

PubMed2002

Mechanistic pathways for the photoisomerization reaction of the anchored, tethered chromophore of the photoactive yellow protein and its mutants.

We show by way of physical organic reasoning that the currently known photochemical results of the chromophore of photoactive yellow protein (PYP) are consistent with that expected of a least volume-demanding process for an anchored, tethered chromophore. The primary photoreaction, interestingly, does not appear to involve a hula-twist process. However, the latter might be involved during subsequent transition of dark intermediates. Absorption data of intermediates obtained from a microsecond time-resolved spectroscopic study of three PYP mutants (E46Q, T50V and R52Q) are consistent with the above analyses.

Bacterial Proteins↗

PubMed2003

Treatment of textile dyeing wastewater using UV/solar photofenton oxidation processes.

Colour removal of effluent from textile dyeing and finishing industry is becoming important because of aesthetic as well as environmental concerns. Conventional treatment methods have several limitations. Hence emerging technologies like advanced oxidation processes which were based on generation of hydroxyl free radicals (OH) were investigated. In the present work, photofenton oxidation process was used to treat textile dyeing wastewater and the study was carried out at different Fenton molar ratio's (H2O2/Fe2+) like 25:1, 50:1, 75:1, 100:1. It was found that maximum decolourisation occurred at a fenton molar ration of 50:1 and pH 3. A maximum colour removal of 97% was achieved after a contact time of 30 minutes and 70% COD reduction was observed after a contact time of 60 minutes in UV photofenton oxidation process. Whereas 80% colour removal and 50-55% COD reduction was observed after a contact time of 2 hrs in solar photofenton oxidation process.

Coloring Agents↗

PubMedDate not supplied

[Fluorescence of rhodopsins and its relation to primary processes of light energy transformation].

A new area of the investigation of visual and bacterial rhodopsins--fluorescence spectroscopy of the pigments is discussed. Fluorescence properties are considered in relation to photochemical transformations of the pigments at low temperatures. A number of fluorescent states of the pigments are described. It is shown that the excited states of bacteriorhodopsin and visual rhodopsin are characterized by a series of common features. The analysis of general properties of the pigments excited states allows a conclusion that the singlet excited states take part in the photoreaction. The photoreaction scheme is discussed in which structural changes of the chromophore take place already in the excited state.

Animals↗

PubMed1976

The effect of colchicine on the induction of ornithine decarboxylase by 12-O-tetradecanoyl-phorbol-13-acetate.

The induction of mouse epidermal ornithine decarboxylase, 1 of the earliest and largest phenotypic changes following treatment of mouse skin with the tumor-promoting agent, 12-O-tetradecanoyl-phorbol-13-acetate, can be inhibited by prior administration of colchicine. Maximal inhibition of this enzyme induction was observed when colchicine was injected i.p. 90 or 120 min before promoter treatment, although time intervals up to 20 hr between colchicine and promoter treatment were effective. The effect of colchicine was dose dependent, with a dose as low as 25 nmoles/mouse causing an inhibition of 35%. Other microtubule-disrupting agents, vinblastine, vincristine, and Colcemid, had a similar effect on ornithine decarboxylase activity. However, beta, gamma-lumicolchicine, a photochemical derivative of colchicine with no antimitotic or microtubule-disrupting ability, and cytochalasin B, an inhibitor of microfilament-dependent processes, had no effect. N6, O2'-dibutyryl 3',5'-cyclic adenosine monophosphate, when administered just before colchicine, blocked the inhibitory action of colchicine. The results of these studies suggest that colchicine-sensitive structures, most likely containing microtubules, may be mediating elements between the binding of tumor promoters, perhaps to specific cell surface receptors, and the subsequent induction of ornithine decdaboxylase.

Animals↗

PubMed1984

Acidic proteins of the large ribosomal subunit in Saccharomyces cerevisiae. Effect of phosphorylation.

Three strongly acidic proteins with pIs between 3.0 and 3.5 have been detected and purified from an ammonium-ethanol extract of Saccharomyces cerevisiae ribosomes. The three proteins, called L45, L44, and L44', have a similar amino acid composition, but differences were shown by tryptic peptide analysis. Nevertheless, the three polypeptides show total cross-reaction to antisera raised against one of them. Protein L44' is very unstable in the extract when treated at the basic pH 9.2, due to an enzymatic process not yet clarified. When purified, the protein is, however, stable. In solution, the proteins are present as dimers, as verified by ultracentrifugation, column filtration, and photochemical cross-linking. The tendency to dimerization is much lower in the case of protein L44'. On the average, 3.2 copies of these proteins are detected per ribosome. The proteins are monophosphorylated when present in the ribosome. Phosphorylation seems to regulate the affinity of the polypeptides for the particles because unphosphorylated proteins bind poorly to the ribosomes deprived of the acidic proteins. Since these proteins are unphosphorylated when present in the cytoplasm [Zinker, S. (1980) Biochim. Biophys. Acta 606, 76-82; Sánchez-Madrid, F., Vidales, F. J., & Ballesta, J. P. G. (1981) Eur. J. Biochem. 114, 609-613], a regulatory mechanism of the ribosomal function based on a phosphorylation-dephosphorylation process of the acidic proteins is being studied.

Amino Acids↗

PubMed2003

Reductive electron transfer and transport of excess electrons in DNA.

In principle, DNA-mediated charge transfer processes can be categorized as either oxidative hole transfer or reductive electron transfer. In research on DNA damage, major efforts have focused on the investigation of oxidative hole transfer or transport, resulting in insights on the mechanisms. On the other hand, the transport or transfer of excess electrons has a large potential for biomedical applications, mainly for DNA chip technology. Yet the mechanistic details of this type of charge transfer chemistry were unclear. In the last two years this mechanism has been addressed in gamma-pulse radiolysis studies with randomly DNA-bound electron acceptors or traps. The major disadvantage of this experimental setup is that the electron injection and trapping is not site-selective. More recently, new photochemical assays for the chemical and spectroscopic investigation of reductive electron transfer and electron migration in DNA have been published which give new insights into these processes. Based on these results, an electron-hopping mechanism is proposed which involves pyrimidine radical anions as intermediate electron carriers.

DNA↗

PubMedDate not supplied

Photochemical bleaching of fluorescent glycosylation products.

We have examined the effect of visible light and ultraviolet on the non-enzymatic glycosylation of lysine in vitro. Glucose and L-lysine were mixed and incubated under white light, UV-A, UV-B, or in the dark. During 15 days of incubation in the dark, a heterogeneous mixture of intensely brown chromophores developed, with a dominant fluorescence excitation maximum at 350 nm and emission maxima near 425 nm. The process was delayed or inhibited to a moderate extent by white light, whereas under UV-A and UV-B this effect was more pronounced. We conclude that non-enzymatic glycosylation can be photochemically modulated by both visible light and ultraviolet.

Fluorometry↗

PubMedDate not supplied

Photochemical behavior of 6-methylpterin in aqueous solutions: generation of reactive oxygen species.

Pterins are a family of heterocyclic compounds present in a wide range of living systems that participate in relevant biological functions and are involved in different photobiological processes. 6-Methylpterin (MPT) was investigated for its efficiency of singlet-oxygen (1O2) production and quenching in aqueous solution. The quantum yields of 1O2 production (phi(delta)) was determined by measurements of the 1O2 luminescence in the near-infrared upon continuous excitation of the sensitizer. Values of phi(delta) were found to be 0.10 +/- 0.02 and 0.14 +/- 0.02 in acidic and alkaline media, respectively. Studies of the photooxidation of MPT in acidic (pH = 5.0-6.0) and alkaline (pH = 10.2-10.8) aqueous solutions at 350 nm and room temperature have been performed. The photochemical reactions were followed by UV-visible spectrophotometry, high-performance liquid chromatography and an enzymatic method for H2O2 determination. MPT is not light sensitive in the absence of oxygen, but it undergoes a photooxidation reaction in the presence of oxygen, yielding several nonpteridinic products. The quantum yields of MPT disappearance were determined and values of 2.4 (+/-0.5) x 10(-4) and 8.1 (+/-0.8) x 10(-4) were obtained in acidic and alkaline media, respectively. H2O2 was detected and quantified in irradiated solutions of MPT. The rate constant of the chemical reaction between 1O2 and MPT (k(r)) was determined to be 4.9 x 10(6) M(-1) s(-1) in alkaline medium and the role of 1O2 in the photooxidation of MPT is discussed.

Pterins↗

PubMed2001

Photoisomerization in rhodopsin.

This article reviews the primary reaction processes in rhodopsin, a photoreceptive pigment for twilight vision. Rhodopsin has an 11-cis retinal as the chromophore, which binds covalently with a lysine residue through a protonated Schiff base linkage. Absorption of a photon by rhodopsin initiates the primary photochemical reaction in the chromophore. Picosecond time-resolved spectroscopy of 11-cis locked rhodopsin analogs revealed that the cis-trans isomerization of the chromophore is the primary reaction in rhodopsin. Then, generation of femtosecond laser pulses in the 1990s made it possible to follow the process of isomerization in real time. Formation of photorhodopsin within 200 fsec was observed by a transient absorption (pump-probe) experiment, which also revealed that the photoisomerization in rhodopsin is a vibrationally coherent process. Femtosecond fluorescence spectroscopy directly captured excited-state dynamics of rhodopsin, so that both coherent reaction process and unreacted excited state were observed. Faster photoreaction of the chromophore in rhodopsin than that in solution implies that the protein environment facilitates the efficient isomerization process. Such contributions of the protein residues have been monitored by infrared spectroscopy of rhodopsin, bathorhodopsin, and isorhodopsin (9-cis rhodopsin) at low temperatures. The crystal structure of bovine rhodopsin recently reported will lead to better understanding of the mechanism in future.

Amino Acid Sequence↗

PubMed1998

Light-driven production of ATP catalysed by F0F1-ATP synthase in an artificial photosynthetic membrane.

Energy-transducing membranes of living organisms couple spontaneous to non-spontaneous processes through the intermediacy of protonmotive force (p.m.f.)--an imbalance in electrochemical potential of protons across the membrane. In most organisms, p.m.f. is generated by redox reactions that are either photochemically driven, such as those in photosynthetic reaction centres, or intrinsically spontaneous, such as those of oxidative phosphorylation in mitochondria. Transmembrane proteins (such as the cytochromes and complexes I, III and IV in the electron-transport chain in the inner mitochondrial membrane) couple the redox reactions to proton translocation, thereby conserving a fraction of the redox chemical potential as p.m.f. Many transducer proteins couple p.m.f. to the performance of biochemical work, such as biochemical synthesis and mechanical and transport processes. Recently, an artificial photosynthetic membrane was reported in which a photocyclic process was used to transport protons across a liposomal membrane, resulting in acidification of the liposome's internal volume. If significant p.m.f. is generated in this system, then incorporating an appropriate transducer into the liposomal bilayer should make it possible to drive a non-spontaneous chemical process. Here we report the incorporation of F0F1-ATP synthase into liposomes containing the components of the proton-pumping photocycle. Irradiation of this artificial membrane with visible light results in the uncoupler- and inhibitor-sensitive synthesis of adenosine triphosphate (ATP) against an ATP chemical potential of approximately 12 kcal mol(-1), with a quantum yield of more than 7%. This system mimics the process by which photosynthetic bacteria convert light energy into ATP chemical potential.

Adenosine Triphosphate↗

PubMed1992

Phototoxicity of non-steroidal anti-inflammatory drugs: in vitro testing of the photoproducts of Butibufen and Flurbiprofen.

In this work, the phototoxicity of two non-steroidal anti-inflammatory drugs, Butibufen and Flurbiprofen, was examined. Both were unstable to light, to give several photoproducts which were isolated and identified. The different photoproducts were formed by a primary photochemical mechanism which involves an initial cleavage of the C-C bond alpha to the carbonyl group, followed by several secondary processes. The cytotoxic effects of the xenobiotics were evaluated using two well-established biological in vitro tests: (a) enzyme leakage lactate dehydrogenase and glutamate-oxaloacetate transaminase from cultured fibroblasts and (b) lysis of red blood cells. The benzylic alcohols caused extensive leakage from cultured fibroblasts at the different concentrations assayed. The alcohol obtained from Butibufen was a potent lytic agent for human red blood cells. The other photoproducts, Butibufen and Flurbiprofen did not produce observable toxic effects on cells.

3T3 Cells↗

PubMed2003

Spectroscopic and mutational analysis of the blue-light photoreceptor AppA: a novel photocycle involving flavin stacking with an aromatic amino acid.

The flavoprotein AppA is a blue-light photoreceptor that functions as an antirepressor of photosynthesis gene expression in the purple bacterium Rhodobacter sphaeroides. Heterologous expression studies show that FAD binds to a 156 amino acid N-terminal domain of AppA and that this domain is itself photoactive. A pulse of white light causes FAD absorption to be red shifted in a biphasic process with a fast phase occurring in <1 micros and a slow phase occurring at approximately 5 ms. The absorbance shift was spontaneously restored over a 30 min period, also in a biphasic process as assayed by fluorescence quenching and electronic absorption analyses. Site-directed replacement of Tyr21 with Leu or Phe abolished the photochemical reaction implicating involvement of Tyr21 in the photocycle. Nuclear magnetic resonance analysis of wild-type and mutant proteins also indicates that Tyr21 forms pi-pi stacking interactions with the isoalloxazine ring of FAD. We propose that photochemical excitation of the flavin results in strengthening of a hydrogen bond between the flavin and Tyr 21 leading to a stable local conformational change in AppA.

Amino Acid Sequence↗

PubMed2006

Superoxide-mediated dissolution of amorphous ferric oxyhydroxide in seawater.

We have investigated the kinetics of superoxide-mediated dissolution of amorphous ferric oxyhydroxide (AFO) in seawater by spectrophotometrically examining the rate of formation of a ferrous-ferrozine complex (Fe(II)(FZ)3) with particular attention given to the effect of aging and iron concentration on the rate of superoxide-mediated dissolution of AFO. The production rates of Fe(II)(FZ)3 decreased with aging of AFO for iron concentrations from 50 to 500 nM, indicating that changes to the chemical and physical properties of AFO affected the reactivity of inorganic ferric iron species with superoxide. A kinetic model developed by assuming that Fe(II)' formation is preceded by the thermal dissolution of AFO provided a good description of the Fe(II)(FZ)3 production rates over time. First-order rate constants for Fe(II)' formation were found to depend on the total iron concentration, suggesting that superoxide-mediated Fe(II) reduction is affected not only by the rate of thermal dissolution of AFO but also by the rate of AFO precipitation. The reported high rates of superoxide production by both photochemical and biotic pathways in aquatic systems coupled with the ability of superoxide to dissolve freshly formed ferric oxides suggest that this process may have a significant impact on the biogeochemical cycling of iron, especially if organisms have an affinity for ferrous iron.

Ferric Compounds↗

PubMed2004

A simple model for estimating emissions of volatile organic compounds from grass and cut grass in urban airsheds and its application to two Australian cities.

Grass, and particularly cut grass, recently has been shown to emit significant amounts of volatile organic compounds (VOCs) into the atmosphere. Some components of these emissions are highly reactive and may contribute to photochemical smog in urban areas. A simple model for estimating the VOC emissions from grass and for grass cutting that allows these processes to be included in urban/regional emissions inventories is presented here. Using previous work and recent literature values, estimates are made of these biogenic volatile organic compound (BVOC) emissions for two typical urban airsheds, those including the cities of Sydney and Melbourne in Australia. Grass and cut grass could contribute approximately 2% for Sydney and 3% for Melbourne of the total VOCs emitted into these urban atmospheres annually. These contributions could rise to 4 and 5%, respectively, during the weekends of the summer growing season and, thus, could contribute to weekday/weekend ozone differences. It is recommended that the emissions of BVOCs from grass and cut grass be included in urban and global emissions inventories so that more accurate predictions of smog chemistry can be determined.

Australia↗

PubMed2005

Polarization multiplexed write-once-read-many optical data storage in bacteriorhodopsin films.

In polymeric films of bacteriorhodopsin (BR) a photoconversion product, which was named the F620 state, was observed on excitation of the film with 532 nm nanosecond laser pulses. This photoproduct shows a strong nonlinear absorption. Such BR films can be used for write-once-read-many (WORM) optical data storage. We demonstrate that a photoproduct similar or even identical to that obtained with nanosecond pulses is generated on excitation with 532 nm femtosecond pulses. This photoproduct also shows strong anisotropic absorption, which facilitates polarization storage of data. The product is thermally stable and is irretrievable to the initial B state either by photochemical reaction or through a thermal pathway. The experimental results indicate that the product is formed by a two-photon absorption process. Optical WORM storage is demonstrated by use of two polarization states, but more polarization states may be used. The combination of polarization data multiplexing and extremely short recording time in the femtosecond range enables very high data volumes to be stored within a very short time.

Journal Article↗

PubMedDate not supplied

[Long-distance transportation of atmospheric pollutants and its effects on ecosystems].

It was known, as far back as the nineteenth century, that rain water from industrial areas was more acid than that from rural areas. The potential risks for life in general were discussed, but no further attention was paid to the issue. At the end of the twentieth century, the ecosystems of Europe, Canada and the United States have been severely damaged by pollutants borne by atmospheric winds to places distant from their origin. The main effects of these atmospheric pollutants are due to sulfur and nitrogen oxide dilution and to photochemical reactions. International organizations have been formed and agreements pronounced and ratified by many countries for a universal study on the pollution process, on the transport of pollutants--mostly sulfur, nitrogen and ozone--and on how to collaborate in order to reduce emissions in the respective countries of origin for the worldwide profit.

Air Pollutants↗