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At least 379 records · Page 21Linked to original sources
PubMed2004

Evaluation of Hypocrellin B in a human bladder tumor model in experimental photodynamic therapy: biodistribution, light dose and drug-light interval effects.

Hypocrellin B (HB), a monomeric perylenequinone pigment, is a promising second-generation photosensitizer for photodynamic therapy. We have evaluated the efficacy of HB mediated PDT by experimenting with various drug-light intervals, based on the biodistribution analysis in human bladder tumor (MGH cell line) models. Tumor growth rates were assessed at 10-day post treatment followed by morphometric analysis. Biodistribution of HB was evaluated using spectrofluorophotometry analysis (Ex: 480 nm, Em: 620-630 nm). The level of HB peaked at 6 h postinjection in tumor, peritumoral skin and normal muscle followed by a decline over the next 42 h. Concurrently, the ratio of drug in tumor versus skin was relatively low at all times in comparison to tumor to muscle ratio. In serum, concentration of HB peaked at 1 h. Almost 88% of its original uptake level was cleared at 48 h. The level of PDT response revealed a strong dependence on the drug-light intervals (DLI) and light dose. For both high and low fluence/fluence rate, comparable tumor response was observed at 1 h DLI; treated tumors exhibited significant tumor regression compared to 6 and 24 h DLI. The absence of tumor response was observed at 24 h DLI even at high light dose (100 J/cm(2); 100 mW/cm(2)). Tumor response detected at low light dose (12 J/cm(2); 12 mW/cm(2)) at short DLI suggests that the tumor vasculature is a more sensitive target compared to the cellular compartment of the tumor, correlating significantly with the bioavailability of the drug in serum. Therefore, HB mediated PDT effect is characteristics of a predominantly vascular mediated effect. This study confirms that for short drug-light intervals, PDT seems to target tumor vasculature, which contributes to tumor destruction.

Animals↗
PubMed1986

Comparison of an experimental updraft ultraviolet light trap with the CDC miniature light trap and biting collections in sampling for Anopheles albimanus in Haiti.

Three methods of capturing Anopheles albimanus mosquitoes were compared during a field study in four villages in northern Haiti. Updraft ultraviolet (UV) light traps proved to be more effective than biting collections, regardless of season or whether the tests were done indoors or outdoors. Biting collections were in turn more effective than the Centers for Disease Control (CDC) miniature light traps. Updraft UV light traps and biting collections yielded more An. albimanus outdoors than indoors; the reverse was found for the CDC miniature light traps. The updraft UV light traps caught An. albimanus on 86% of the occasions used outside and 75% of the occasions inside. The biting collections were equally as successful as the traps in catching mosquitoes outside but caught An. albimanus only on 64% of the occasions when used inside houses. The CDC miniature light traps were successful in collecting An. albimanus on 33% of the occasions outside and 60% of the occasions inside.

Animals↗
PubMed1983

[Lightness decrease of the total area accompanying simultaneous lightness contrast].

Matches to the Munsell Lightness Scale were made in the two areas in a contrast-inducing pattern whose luminance difference was less than about 10%, and were compared with those of two uniform luminance field of corresponding luminances. The results showed (1) the simultaneous lightness contrast appeared in the contrast-inducing pattern, (2) the high luminance area in the contrast-inducing pattern appeared darker than the uniform luminance field of the same luminance. The lightness decrease in the high luminance area could be explained neither by Békésy's neural units model nor by Stevens' power transformation model, since Békésy's model predicts that high luminance area should appear lighter than the corresponding uniform luminance pattern, while Stevens' model expected the identical lightnesses between the two areas. In order to explain both the simultaneous lightness contrast and the lightness decrease, it was introduced a new model which included not only the antagonistic excitation and inhibition depending upon luminance-intensity, but also the non-antagonistic inhibition which is dependent upon the luminance-difference.

Adult↗
PubMed2002

Involvement of active oxygen species in degradation of light-harvesting proteins under light stresses.

This paper presents evidence for light-mediated degradation of isolated light-harvesting proteins (Lhc2) and involvement of oxygen free radicals in the process. The time course of light harvesting photodestruction is much slower than that of D1 protein (requiring hours for complete breakdown). By use of mass spectrometry and amino acid sequencing, it has been revealed that the primary cleavages take place in the hydrophilic portion of the NH(2) region where oxygen-containing radicals attack randomly and not at specific sites. Moreover, these chlorophyll binding proteins are completely fragmented. From the effectiveness of scavengers and the preliminary electron paramagnetic resonance measurements reported, it appears that singlet oxygen is involved as a short-lived species, and hydroxyl and alkoxyl radicals act at higher light intensity or over a longer time, whereas hydrogen peroxide and superoxide anions are not observed. Antenna proteins appear more resistance to photodestruction in their monomeric form than in trimeric form, while minor antenna are highly sensitive. However, the organization of both minor and major proteins in the photosystem II supracomplex affords some photoprotection. Interestingly, leaves exposed to strong light contained degraded major antenna, unlike those kept in the dark, which is consistent with studies on the illumination of isolated proteins, supporting the hypothesis that active oxygen species play a role in vivo in the short-term acclimative adaptation of plants.

Amino Acid Sequence↗
PubMed1999

Characterization of the different peripheral light-harvesting complexes from high- and low-light grown cells from Rhodopseudomonas palustris.

In this paper we demonstrate that the spectroscopically different peripheral light-harvesting complexes from Rhodopseudomonas palustris, strain 2.6.1, isolated from high- and low-light grown cells have widely differing bacteriochlorophyll a (BChl a) resonance Raman spectra in the high-frequency carbonyl region (1550-1750 cm-1). Complexes synthesized in low-light grown cells exhibit Raman spectra characteristic of B800-850 and B800-820 complexes, depending on the excitation conditions. The in vivo strategy for low-light adaptation in this bacterium is thus somewhat different from that generally encountered in the Rhodospirillaceae. In these bacteria, as typified by Rps. acidophila and Rps. cryptolactis, low-light conditions induce the synthesis of B800-820 only complexes in which the hydrogen bonds between the acetyl carbonyl and the B850 binding pocket are broken, inducing changes in the absorption properties of the monomeric bacteriochlorophylls. In the case of Rps. palustris, additional spectral effects occur due to the coupling of the electronic levels of the differently interacting dimers. The extensive use of differential alpha/beta-polypeptide expression [Tadros et al. (1993) Eur. J. Biochem. 217, 867-875] thus allows Rps. palustris to alter its BChl a binding site environments causing the observed spread of BChl a Qy transitions, ranging from 801 to 856 nm.

Bacteriochlorophylls↗
PubMed1982

Purification of gizzard myosin light-chain phosphatase, and reversible changes in the ATPase and superprecipitation activities of actomyosin in the presence of purified preparation of myosin light-chain phosphatase and kinase.

Sepharose 4B conjugated with phosphorylated myosin light chains was used in affinity chromatography of a partially purified preparation of gizzard myosin light-chain phosphatase (MLCP) (Onishi et al. (1979) J. Biochem. 86, 1283-1290). The MLCP preparation thus purified contained, according to SDS gel electrophoresis, three components of 67,000 (67 K), 54,000 (54 K), 34,000 (34 K) daltons. In an accompanying report, Uchiwa et al. (J. Biochem. 91, 273-282 (1982)) described the purification of gizzard myosin light-chain kinase, which consisted of two subunits; 130 K and 17 K daltons. Using the purified preparations of MLCP and MLCK, it was demonstrated a) that reversible changes in the ATPase and superprecipitation activities occur as myosin light chains are enzymatically phosphorylated and dephosphorylated, and b) that addition of a very low concentration of Ca2+ and its removal cause reversible changes in the turbidity of actomyosin suspensions as well as in the state of phosphorylation of myosin light chains only when MLCK and MLCP are both present. These results provide strong support for the proposal (see Ikebe et al. (1977) J. Biochem. 80, 299-302) that MLCK and MLCP play a key role in the Ca2+ regulation in gizzard.

Actomyosin↗
PubMed2004

High-intensity-light-dependent and transient expression of new genes encoding distant relatives of light-harvesting chlorophyll-a/b proteins in Chlamydomonas reinhardtii.

We identified four Lhc-like genes (Lhl) encoding proteins that are distant relatives of light-harvesting chlorophyll a/b-binding (LHC) proteins in the green alga Chlamydomonas reinhardtii. Their mRNA levels after transfer from low-intensity light to high-intensity light (HL) were examined and compared with those of Lhc genes encoding LHC proteins of PSII. The transfer caused a decrease in the mRNA level of Lhl3, a homolog of Arabidopsis thaliana Lil3, within 2 h, followed by gradual restoration depending on the intensity of HL. The response was similar to that of Lhc genes. In contrast, the mRNA levels of Lhl1, Lhl2 and Lhl4 significantly increased, reached a maximum within 1 h after the transfer and then rapidly returned to a low level. The intensity of HL little influenced the response of these genes. While the Lhl1 and Lhl2 proteins were homologs of early light-inducible protein (ELIP) and high-light-inducible protein (HLIP), respectively, Lhl4 encoded a novel protein. The HL-induced expression of Lhl4 was most prominent among the genes tested. Studies using various inhibitors indicate that the HL response is not mediated by the redox state of plastoquinone pool or reactive oxygen species, but required de novo protein synthesis in the cytosol.

Amino Acid Sequence↗
PubMed1984

The sources of light and lighting at work.

Succeeding in lighting industrial, office and other work environments is dependent on many factors. Good result is not guaranteed if only one of these factors is taken into account. It is essential to choose appropriate light sources and use them correctly for different tasks. Although the amount of light and its composition is considered satisfactory for a certain task, glare and reflected glare still cause inconvenience in the work places making the performance of visual tasks difficult. The lux and luminance levels of the work areas regulate the size of the observer's pupils. The size of the pupil determines for its part how easily and quickly eyes can be accommodated for a sight distance. The indirect disadvantages caused by poor visual conditions are often significant. For example at display work reflected glare does not only slow down reading. The effort to avoid the reflections from the screen by changing the direction of observation effects the working positions. Inconvenient posture may cause pains in the neck and back. In lighting design the problems of age vision are taken into account. We should also bear in mind the significance of the colour of light when considering these problems.

Accident Prevention↗
PubMedDate not supplied

Light output of disposable vs. nondisposable curing light tips following high-level disinfection.

Following a pilot study which determined that autoclaving a disposable tip resulted in physical deformation, rendering the tip ineffective for photocuring, this study evaluated the effects of two FDA-cleared high-level disinfectants on the light output and physical integrity of disposable and nondisposable curing light tips. Nine disposable and five nondisposable curing tips were immersed in each of the two disinfectants. No significant differences (p > 0.05) in light output over time were observed for either type of curing light tip in either solution. None of the tips were physically affected by immersion and light output values remained in the acceptable range for resin composite polymerization.

Composite Resins↗
PubMed1975

Voluntary exposure to light by young and aged albino and pigmented inbred mice as a function of light intensity.

Young (5 month) and old mice (23 and 26 months) of the inbred A/J and C5BL/6J strains (N = 80) were isolated in ventilation chambers with ad lib food and water for 1 week at a time. Each animal was allowed to select its own lighting schedule by pressing one lever to turn on a light of either 10.76 or 166.40 lux illumination and pressing another lever to turn the light off. Three-way analyses of variance for Age, Strain, and Illumination effects on parameters of bar pressing, stimulus change, and light duration patterns per circadian period (24 hr) indicate that old mice are less active than young mice and the A/J mice are less active than C57BL/6J mice. Young mice spent more time in the dark than old mice and the A/J albino mice spent more time in the dark than did the C57BL/6J pigmented mice. Other age and strain differences were noted as well and are discussed with respect to some theories of light exposure by nocturnal animals.

Aging↗
PubMed1979

Predictive value of the analogy between hormone-sensitive adenylate cyclase and light-sensitive photoreceptor cyclic GMP phosphodiesterase: a specific role for a light-sensitive GTPase as a component in the activation sequence.

We report experiments which involve a light sensitive GTPase in the light dependent activation of retinal rod 3'5'-cyclic guanosine monophosphate (cGMP) phosphodiesterase (PDE). The data suggest that the light activated GTPase is intermediate between rhodopsin and PDE in the light-dependent activation sequence. We list the many striking similarities between hormone sensitive adenylate cyclase and light activated PDE in order to emphasize that the findings presented herein may have predictive value for ongoing studies of the hormone sensitive adenylate cyclase specifically regarding the role of the hormone activated GTPase in the activation sequence.

3',5'-Cyclic-GMP Phosphodiesterases↗
PubMed1991

Expression of circadian rhythmicity in Djungarian hamsters under constant light: effects of light intensity and the circadian system's state.

Djungarian hamsters (Phodopus sungorus), were exposed to constant light with increasing intensities (20, 60, 350 lux), and wheel running activity was recorded. With increasing light intensity the percentage of hamsters showing a split in their daily activity pattern increased and the free running period was lengthened for both the unsplit and the split state. The fact that the free running period of both states depended on the light intensity together with the observation that the highest incidence of a circadian activity occurred under 350 lux, provoked the idea that the emergence of splitting or a circadian rhythmicity is a direct consequence of the light induced lengthening of the free running period. However, analysis of the data failed to support the idea that emergence of a split or a circadian activity is a threshold phenomenon with respect to the free running period. Due to differences in circadian function some Djungarian hamsters do not exhibit photoinduction following short day exposure. In these individuals splitting also occurred but required exposure to a higher light intensity than in photo-responsive hamsters. This observation is in accordance with the idea that the two phenotypes differ in the interaction of the two component oscillators underlying circadian rhythmicity.

Animals↗
PubMed2000

Light-harvesting complex II pigments and proteins in association with Cbr, a homolog of higher-plant early light-inducible proteins in the unicellular green alga Dunaliella.

Like higher plants, unicellular green algae of the genus Dunaliella respond to light stress by enhanced de-epoxidation of violaxanthin and accumulation of Cbr, a protein homologous to early light-inducible proteins (Elips) in plants. Earlier studies indicated that Cbr was associated with the light-harvesting complex of photosystem II (LHCII) and suggested it acted as a zeaxanthin-binding protein and fulfilled a photo-protective function (Levy et al. 1993, J. Biol. Chem. 268: 20892-20896). To characterize the protein-pigment subcomplexes containing Cbr in greater detail than attained so far, thylakoid membranes from Dunaliella salina grown in high light or normal light were solubilized with dodecyl maltoside and fractionated by isoelectric-focusing. Analysis of the resolved LHCII subcomplexes indicated preferred associations among the four LHCIIb polypeptides and between them and Cbr: subcomplexes including Cbr contained one or two of the more acidic of the four LHCIIb polypeptides as well as large amounts of lutein and zeaxanthin relative to chlorophyll a/b. After sucrose gradient centrifugation, Cbr free of LHCIIb polypeptides was detected together with released pigments; this Cbr possibly originated in subcomplexes dissociated in the course of the analysis. These results agree with the conclusion that Cbr is part of the network of LHCIIb protein-pigment complexes and suggest that the role played by Cbr involves the organization and/or stabilization of assemblies highly enriched in zeaxanthin and lutein. Such assemblies may function to protect PSII from photodamage due to overexcitation.

Centrifugation, Density Gradient↗
PubMed1985

Characterization of light-harvesting mutants of Rhodopseudomonas sphaeroides. I. Measurement of the efficiency of energy transfer from light-harvesting complexes to the reaction center.

Light-harvesting mutants of Rhodopseudomonas sphaeroides lacking either the B800-850 complex or the B875 complex have been characterized by their absorption spectra in the visible and near-infrared region, and by their ability to transfer energy from the light-harvesting complexes to the reaction center. A new method of measuring the relative efficiency of energy transfer from the light-harvesting complexes to the reaction center is described. The B875- mutant had absorption maxima in the near-infrared at 800 and 849 nm with no evidence of an 875-nm shoulder. The efficiency of energy transfer from the light-harvesting complexes to the reaction center in the B875- mutant was 24% of the value measured for the wild-type strain and the B800-850- mutant. Yet, despite the fact that the efficiency of energy transfer for the B800-850- mutant and the wild-type strain were the same, there was a large difference in their photosynthetic unit size. These results are discussed in the context of a model in which light energy captured by the B800-850 complexes is transferred through the B875 complexes to the reaction center.

Bacterial Proteins↗
PubMed1985

Light scattering of whole excised human cataractous lenses. Relationships between different light scattering parameters.

The light scattering intensities of 27 cataractous human lenses were obtained as a function of scattering angle. Unpolarized white light (tungsten) and polarized light of Hg lamp at 435.8 and 546.1 nm were used in the I parallel and I+ modes. Selected light scattering parameters such as relative scattering intensities (I45/I0), dissymmetry ratio (I135/I45) and depolarization ratios (I45/I0)+/(I45/I0) parallel were correlated with the age of lens with percent transmission using regression analysis. Excess scattering functions were calculated that quantitatively describe the quality of lens. These excess functions were also correlated with other scattering parameters. A method which can be used to estimate the light intensity that reaches the retina at different scattering angles for a cataractous lens once the back scatter intensity (slit lamp examination) is known is given.

Adult↗
PubMed1985

Two-site phosphorylation of the phosphorylatable light chain (20-kDa light chain) of chicken gizzard myosin.

When prepared under specified conditions chicken gizzard myosin was obtained which when incubated with ATP gave rise to a diphosphorylated as well as the monophosphorylated form of P light chain. Formation of the diphosphorylated light chain occurred more readily with these myosin preparations, but could also be obtained by prolonged incubation of the isolated whole light chain fraction with kinase preparations from rabbit skeletal and chicken gizzard muscles. Using isolated light chains as substrate the more readily formed monophosphorylated light chain contained serine phosphate while the diphosphorylated form contained serine and threonine phosphates.

Adenosine Triphosphate↗
PubMed1988

The induction of chromosomal aberrations and SCE by visible light in combination with dyes. I. The effect of hypoxia during light exposure in unsynchronized Chinese hamster ovary cells, sensitized with acridines.

A comparison has been made between the ability of different acridine compounds to act as sensitizers for visible light (400-700 nm) induced chromosomal aberrations and sister-chromatid exchanges (SCE) in unsynchronized Chinese hamster ovary (CHO) cells. Cells were treated for 20 min with acridines (0.1-5.0 microgram/ml), washed free of excess dye and subsequently exposed to visible light (2 x 40 W/8 W m-2) either in air or in nitrogen for 5-15 min. The 4 acridines tested, proved to be effective sensitizers for the induction of both chromosomal aberrations and SCE by visible light. The most pronounced effect was observed when the light exposure of the fluorochrome-pretreated cells was performed in air. Hypoxic conditions during light exposure reduced the effect dramatically, especially in the case of induced chromosomal aberrations. The order of efficiency for the induction of both chromosomal aberrations and SCE was acridine orange greater than acridine yellow greater than proflavine greater than 3,6-diamino-10-methylacridine. The results are discussed in terms of S-independent versus S-dependent mechanisms for inducing chromosomal alterations and the potential involvement of oxygen-derived free radicals in this process.

Acridine Orange↗
PubMed1980

Activity of multiple light chain genes in murine myeloma cells producing a single, functional light chain.

Two cloned lambda 1-producing myelomas (HOPC-1, MOPC-104E) contain rearranged kappa genes and levels of mature-sized kappa RNA comparable to those found in kappa-producing myeloma cells. Another lambda 1-producing myeloma tumor line (HOPC-2020) and a lambda 1-containing B cell leukemia line (BCL1) also contain significant levels of kappa RNA. One lambda 11-producing line (MOPC-315) contains no detectable kappa RNA, but it also has no kappa genes in the embryonic configuration. kappa-related proteins are not detectable in the lambda 1-producing lines by standard procedures, but by sensitive methods at least two lines contain kappa protein fragments. The MOPC-104E line produces both a 14.5K kappa fragment that is not readily detectable because of its low rate of synthesis and short half-life (T 1/2 less than 5 min), and a major 16.5K protein that lacks kappa cross reactivity but is demonstrable by translation of purified MOPC-104E kappa RNA. The HOPC-1 kappa RNA also encodes a short-lived 14K kappa fragment. The MPC-11 line, which produces a mature kappa RNA and protein as well as an 800 base kappa fragment RNA and kappa protein fragment, has both kappa alleles rearranged, one apparently aberrantly between J and C kappa. Two different kappa RNA species, one the same size as the MPC-11 kappa fragment RNA, frequently are present in kappa RNA-containing Abelson murine leukemia virus-transformed lymphoid cells as well as in 18 and 19 day murine fetal liver. For light chains, neither allelic nor isotype exclusion is generally evident in myeloma and lymphoma cells; rather both produce only a single functional light chain. Models of light chain activation must explain restriction by considering the functional properties of the light chain rather than light chain gene expression.

Animals↗