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PubMed1980

Photodestruction of acetylcholinesterase.

Ultraviolet irradiation of 11S acetylcholinesterase (acetylcholine acetylhydrolase, EC 3.1.1.7) produces a loss of tryptophan fluorescence which is best described as the sum of two separable first-order processes, one much more rapid than the other. In addition, the enzyme undergoes an all-or-none inactivation that is monotonically first order. Simultaneous with activity loss, photoscission takes place and results in a molecular weight drop of 1 x 10(5); this decrease is first order with a rate constant identical to that for enzymatic inactivation. These processes are accompanied by apparent conformational changes, as shown by circular dichroic and difference absorption spectra. The relative photochemical inactivation efficiency of incident light is unity when corrected for the wavelength dependence of fluorescence excitation, which is consistent with an efficient Förster resonance transfer of energy among the aromatic chromophores. The extreme sensitivity of acetylcholinesterase to photodestruction upon photon absorption and the several events that follow it not only suggest that these findings might be a basis for a useful molecular probe of the structure of this enzyme, but also indicate that additional care should be taken when conducting spectroscopic studies in the UV region.

Acetylcholinesterase↗

PubMed1995

Using cell-fractionation and photochemical crosslinking methods to determine the cellular binding site(s) of the antitumor drug DMP 840.

In order to understand its mechanism of action we have begun an effort to better define the cellular target of action of the experimental antitumor agent DMP 840 (NSC D640430; (R,R)-2,2'-(1,2-ethanediylbis(imino-(1-methyl-2,1-ethanediyl)))-bi s(5- nitro-1H-benz(de)isoquinoline-1,3-(2H)-dione) dimethanesulfonate). Using a combination of gentle cell fractionation procedures and a previously unidentified photochemical crosslinking reaction, we have shown that after the drug is added to cultured Clone A cells, more than 80% of the drug that is found associated with cells partitions to the chromatin-containing structural framework of the cell and that the primary target after crosslinking with 360 nm light is DNA. While DMP 840 photoreacts quite efficiently with purified RNA in vitro, no photoattachment of the drug to RNA was observed in cells. In vitro photochemical studies also reveal that while GC-rich DNA is a preferred target for drug interaction, AT-rich DNA is more active in the photochemical crosslinking reaction. These results suggest that DMP 840 probably kills cells by interfering with DNA-metabolic processes, and that the drug and its derivatives are likely to be useful photoactive molecular probes for investigating higher order chromatin structures in cells.

Animals↗

PubMed2006

Photodynamic therapy of microbial infections: state of the art and perspectives.

Photodynamic therapy (PDT) is coming of age as an efficient alternative treatment for microbial infections, a problem which is presently aggravated by the increasingly widespread diffusion of antibiotic-resistant microbial strains. In particular, the use of red light-absorbing photosensitizers as photodynamic antimicrobial agents is characterized by various favorable features, including: (a) the broad spectrum of antimicrobial action of selected phenothiazines, porphyrins, and phthalocyanines, which promote the photosensitized inactivation of Gram(+) and Gram(-) bacteria, fungi, mycoplasma, and parasites by using one phototherapeutic protocol and mild irradiation conditions; (b) porphyrins/phthalocyanines display no appreciable toxicity in the dark at photochemically active doses; (c) microbial cell death is primarily a consequence of membrane photodamage through a typically multitarget process, which minimizes the risk of both the onset of mutagenic processes and the selection of photoresistant cells; (d) such photosensitizers act with essentially identical efficiency against both wild and antibiotic-resistant strains, whereas no selection of photoresistant microbial pathogens has been observed; (e) a combination between antibiotic-based and photodynamic therapy is possible. A typical example of phthalocyanine-sensitized photoinactivation of methicillin-resistant Staphylococcus aureus (MRSA) is provided. At present, antimicrobial PDT appears to be especially convenient for the treatment of localized infections, such as oral candidosis, periodontitis or chronic wounds.

Animals↗

PubMed2006

Treatment of oily port wastewater effluents using the ultraviolet/hydrogen peroxide photodecomposition system.

This paper presents the nonselective degradation of mechanically pretreated oily wastewater by hydrogen peroxide (H2O2) in the presence and absence of UV irradiation. The effect of chemical oxidation on wastewater biodegradability was also examined. The exclusive use of H2O2 photolyzed by daylight results in quite efficient degradation rates for the low peroxide concentrations used. Higher hydrogen peroxide concentrations inhibit degradation of organic contaminants in the wastewater. The degradation rates of all contaminants are relatively high with an advanced oxidation system (UV/H2O2), but degradation efficiencies are not distinguishably different when 20 or 45 minutes of UV irradiation is used. The excess of H2O2 used in the process can inhibit phenolic degradation and may lead to the formation of a new phenolic fraction. The biodegradability of port wastewater did not increase significantly following the application of the advanced oxidation process.

Biodegradation, Environmental↗

PubMed1989

The ribonucleoprotein structures along the pathway of mRNA formation.

Heterogeneous nuclear RNAs (hnRNAs), some of which are mRNA precursors, and the mature mRNAs are associated in eukaryotic cells with specific proteins to form ribonucleoprotein complexes (RNP). The RNP proteins are likely to play a major role in the formation, packaging, processing, and function of mRNA. The major proteins that interact with hnRNA and with mRNA were identified by photochemical RNA-protein cross-linking in intact cells and monoclonal antibodies to several of these proteins were produced. Using these antibodies the hnRNP proteins were characterized and the hnRNP complex was isolated from vertebrate cell nuclei. The hnRNP complex is a unitary structure of consistent, defined and conserved components. The proteins of the hnRNP complex were identified and the general organization of hnRNA and proteins in the hRNP complex were studied.

Animals↗

PubMed2001

Facilitation of cleaning of alumina surfaces fouled with heat-treated bovine serum albumin by ozone treatment.

Facilitation of cleaning of alumina (A12O3) particles fouled with heat-treated bovine serum albumin (BSA), which contains sulfhydryl groups on the molecule, by gaseous ozone was studied. With increasing temperature of heat treatment, the amount of adsorbed BSA onto A12O3 surfaces increased, whereas the rate of BSA desorption during alkali cleaning decreased markedly, resulting in the larger amounts of BSA remaining on 12O3 surfaces. No significant amounts of BSA were removed from A12O3 surfaces by alkali cleaning alone when treated at temperatures above 120 degrees C. Before alkali cleaning, the heat-treated, BSA-fouled AI2O3 at 150 degrees C were treated with 0.05 to 0.30% (vol/vol) gaseous ozone at room temperature. Ozone pretreatment markedly accelerated the rate of BSA desorption during subsequent alkali cleaning. The effect of ozone pretreatment on BSA removal depended on the concentration of ozone and treatment time and hence on the total amount of ozone supplied. The molecular weight (MW) of desorbed BSA during alkali cleaning without ozone pretreatment coincided with the MW of the native BSA, whereas the MW of desorbed BSA during the combined ozone-alkali cleaning was lower than the MW of the native BSA. This indicated that the heat-treated BSA molecules adsorbed on A12O3 were partially decomposed into some fragments by ozone pretreatment, resulting in the facilitation of the removal of BSA during alkali cleaning.

Adsorption↗

PubMed2003

[Photooxidation characteristics of super-hybrid rice "Liangyoupeijiu" and its parents].

With comparison of the differences of light absorption and active oxygen metabolism between super-hybrid rice "Liangyoupeijiu" and its parents, this paper provided a physiological foundation of matching and grouping for cultivating anti-photooxidized hybrid rice. TPS-photosynthetic system and FMS2-fluorescence (Hansatech, UK) were used to respectively determine the photosynthetic rate and the chlorophyll fluorescence in the rice leaves that had been processed in artificial photooxidization. Meanwhile, the contents of chlorophyll, protein and malonaldehydic acid (MDA) as well as the activation of superoxide dismutase (SOD) and peroxidase (POD) were determined. The results showed that the photosynthetic rate of "Liangyoupeijiu" was 2.4% lower than that of its female parent, and 23% higher than that of its male parent. After eight days anti-photooxidization process, its chlorophyll content was higher than that of its female parent by 33%, protein by 15%, initial photochemical efficiency by 30%, SOD by 32% and POD by 100%, while its photochemical quince coefficient was lower than that of its female parent by 9% and MDA by 50%. It showed that there was not much difference between the filial generation and its male parent. The super-hybrid rice "Liangyoupeijiu" was very efficient for solar energy utilization under the condition of photooxidization, and had outgrown its parents in the aspect of anti-photooxidization.

Chimera↗

PubMed1981

[Phases of photoelectrical response of bacteriorhodopsin].

The generation of electrical potential difference by bacteriorhodopsin sheets incorporated into collodium film impregnated with a lecithine solution in decane was studied. The electrical response to a short light flash inducing a single turnover of bacteriorhodopsin consists of four phases. Phase I of photoresponse (tau less than 0.2 mks) has a small amplitude and is directed oppositely to the electrical response to continuous light. The negative phase is followed by positive phases, i.e. microsecond (II) and millisecond (III) ones, either of which can be decomposed at least into two exponents. Phase IV of the electrical response is a passive discharge of capacity of the "bacteriorhodopsin sheets--collodium film" system. Although phases II and III correspond to the generation and disappearance of the photochemical cycle intermediate with an absorption maximum at 412 nm, the parameters and activation energy of these two processes do not show complete coincidence. The effects of gramicidin A and the trifluoromethoxycarbonylcyanidephenylhydrazone uncoupler on the photoelectrical response were analyzed. The data obtained are discussed in terms of an equivalent electrical scheme, according to which the bacteriorhodopsin sheets form closed vesicles upon being incorporated into collodium film.

Bacteriorhodopsins↗

PubMed1993

Age-related macular degeneration: the current understanding of the status of clinicopathology, diagnosis and management.

BACKGROUND: This paper represents an up-to-date review of the current thoughts regarding the etiopathogenesis and management of the various varieties of age-related macular degeneration (ARMD). METHODS: Included is a look at the epidemiology as well as the clinicopathologic basis for the development of the degenerative process. CONCLUSIONS: The clinicopathologic basis for development of ARMD is divided into drusen, lipofuscin development, solar radiation effects, photochemical damage and mediation by antioxidants, choroidal neovascularization, scarification, and retinal pigment epithelial detachment. The clinical presentation of both non-exudative and exudative ARMD is discussed with synopses of the mimickers of both outlined in the text. RESULTS: Current accepted methods of therapy are discussed including; laser intervention, surgical removal of membranes, and investigational modes of treatment including antioxidants. Specific management protocol is discussed based on the current knowledge base.

Aged↗

PubMedDate not supplied

Modification of the frictional surfaces of artificial joints.

To overcome the wear problems associated with artificial joint materials, new surface structures with regular patterning were designed and fabricated. The lubrication properties were studied to evaluate the wear of the frictional surfaces. The surface structure was a pattern of "dents" with a diameter of 0.2-1.0 mm and a pitch of 0.6-2.0 mm. The pattern was fabricated on the stainless steel (SUS) surface by a photochemical etching technique with 3 microns depth, and on an ultrahigh molecular weight polyethylene (UHMWPE) surface by mechanical processes. The time dependent changes of frictional force between SUS and UHMWPE were measured, and the surface morphologic changes were observed. The patterned surface showed lower frictional force than the smooth non-patterned surface, and less wear occurred on the patterned sample than on the sample without a pattern. There were optimum sizes for the diameter and the pitch of the pattern. These results demonstrated that lubrication properties could be improved by patterning of the frictional surfaces. The surface patterning was effective in preventing wear of the frictional surface, and the life of an artificial joint could be extended by such patterning.

Biomechanical Phenomena↗

PubMed1998

Structure and medium-dependent photodecomposition of fluoroquinolone antibiotics.

The photochemical reactivity of four fluoroquinolone antibiotics is examined. For norfloxacin (NOR), enoxacin (ENX) and lomefloxacin (LOM), the only process occurring is defluorination (from position 6 for the first two drugs, from position 8 for the last one). The quantum efficiency is both structure and medium dependent (phi close to 0.5 both in water and in 0.1 M phosphate buffer for LOM; 0.01 for ENX and 0.004 for NOR in buffer, but more than an order of magnitude higher in neat water). Ofloxacin (OFL) is less light sensitive (phi 0.001) and undergoes, in part, reactions different from defluorination. The photoreaction involves heterolytic C-F bond fragmentation and its efficiency is determined by the internal charge-transfer character of the excited state (increasing in the series OFL < NOR < ENX < LOM according to the electronegativity of the substituent in position 8) and by the stabilization of the resulting aryl cation (larger for the 8-cation than for the 6-cation). The relevance of these data for the rationalization of the known phototoxicity of these drugs is discussed.

Anti-Infective Agents↗

PubMed1990

[Progress report. Lipid peroxidation. 1. Primary reactions].

Edible fats and oils are an important component of human nutrition. There are many kinds of changes and destruction of lipids. One of the most important processes is the autoxidation of essential fatty acids. Primary products of oxidation are mono-hydroperoxides of fatty acids formed by three different pathways. Thermal activation of fatty acids will be followed by thermodynamically controlled distribution of the hydroperoxide isomers. With enzymatic or photochemical oxidation specific distribution of isomeric hydroperoxides is observed. These products can be also used for the determination of the type of oxidation which took place. The hydroperoxides formed in the process of oxidation cause a radical chain reaction with a powerful progress of oxidation. The products formed by chain termination are characterized by different stability. These products include the possibility of decomposition and consequent reactions.

Chemical Phenomena↗

PubMed2003

Disassembly and degradation of photosystem I in an in vitro system are multievent, metal-dependent processes.

An in vitro system was created to study the process of membrane protein degradation by using photosystem I (PS1) as a model membrane protein. Purified chloroplast membranes were incubated at 30 degrees C in a defined buffer along with various extracts or reagents to reconstitute the disassembly and degradation of PS1, which was monitored by a variety of techniques that probe the integrity of the PS1 complex: photo-biochemical assays, semi-native gel electrophoresis, low temperature fluorescence spectroscopy, and immunoblots using antibodies against different PS1 subunits. During a typical time course, degradation of PS1 appeared to be a multievent process, with disassembly of the complex preceding proteolysis of the subunits. The first change seen was a rapid (<5 min) decrease in PS1 photochemical activity. This was followed by a diminution of far-red fluorescence emission from the core antenna of PS1 and a slower disassembly of the PS1 chlorophyll-protein core complex, as visualized by semi-native gel electrophoresis. Surprisingly, the latter was not accompanied by a similar rate of proteolysis of the PsaA core subunit. In contrast, addition of soluble proteases caused rapid loss of immuno-detectable PS1 polypeptides and cleavage of the major PS1 polypeptides in interhelical loops. The in vitro degradation process was time- and temperature-dependent but did not require ATP, GTP, or soluble chloroplast proteins. Chelation of divalent cations by EDTA inhibited the later steps of disassembly and proteolysis, and this effect could be reversed by addition of micromolar Zn2+, with Co2+ and Ca2+ providing somewhat lower activity.

Animals↗

PubMed2005

Computational and experimental studies on the mechanism of the photochemical carbonylation of group 6 Fischer carbene complexes.

The photocarbonylation reaction of Group 6 Fischer carbene complexes has been studied by DFT and experimental procedures. The process occurs by intersystem crossing (ISC) from the lowest excited singlet state (S1) to the lowest triplet state (T1), the latter structure being decisive for the outcome of the reaction. Methylenepentacarbonylchromium(0) complexes, alkoxypentacarbonylchromium(0)carbene complexes, and alkoxyphosphinetetracarbonylchromium(0) carbene complexes have coordinatively unsaturated chromacyclopropanone T1 structures with a biradical character. The evolution of the metallacyclopropanone species occurs by a jump (spin inversion) to the S(0) hypersurface by coordination of a molecule of the solvent, leading to ketene-derived products in the presence of ketenophiles or reverting to the starting carbene complex in their absence. The T1 excited states obtained from methylenephosphinetetracarbonylchromium(0) complexes and pentacarbonyltungsten(0)carbene complexes are unable to produce the carbonylation. The reaction with ketenophiles is favored in coordinating solvents, which has been tested experimentally in the reaction of alkoxypentacarbonylchromium(0) complexes and imines.

Journal Article↗

PubMed2003

NMR kinetic investigations of the photochemical and thermal reactions of a photochromic chromene.

The photochromic behavior of 2,2-di(4-fluorophenyl)-6-methoxy-2H-1-chromene has been investigated by 19F NMR spectroscopy. Photocoloration under UV irradiation at low temperature led to the formation of three interconverting photoisomers including two merocyanines and an unprecedented allenyl-phenol isomer. Photobleaching with visible light, which was known to lead to reversion to the initial closed chromene, was shown to increase allenyl-phenol concentration. Thermal relaxation of the preirradiated system was also studied at various temperatures. In each case (UV and visible irradiations, thermal isomerization), the kinetics of each of the four species was monitored. Numerical analysis of concentration vs time profiles enabled us to unequivocally establish the global mechanism occurring in each of the experimental conditions and to interpret the specific reactivity of each photoisomer. It has been shown that, among the 12 possible isomerization processes, only some paths were active. For the first time, it has been possible to determine their corresponding thermal activation parameters and photochemical quantum yield ratios.

Journal Article↗

PubMed2006

Computational studies of the primary phototransduction event in visual rhodopsin.

This Account addresses recent advances in the elucidation of the detailed molecular rearrangements due to the primary photochemical event in rhodopsin, a prototypical G-protein-coupled receptor (GPCR) responsible for the signal transmission cascade in the vertebrate vision process. The reviewed studies provide fundamental insight on long-standing problems regarding the assembly and function of the individual residues and bound water molecules that form the rhodopsin active site, a center that catalyzes the 11-cis/all-trans isomerization of the retinyl chromophore in the primary step of the phototransduction mechanism. Emphasis is placed on the authors' recent computational studies, based on state-of-the-art quantum mechanics/molecular mechanics (QM/MM) hybrid methods, addressing the structural refinement of the retinyl chromophore binding site in high-resolution X-ray structures of bovine visual rhodopsin, the energy storage mechanism, and the molecular origin of spectroscopic changes due to the primary photochemical event.

Isomerism↗

PubMed2006

Computer-aided design of promising photochemical alkoxy radical precursors.

A computer-aided design of alkoxyl radical precursors is performed. The new precursors should combine the advantages of N-alkoxypyridine-2(1H)thiones (less reactive radicals) and N-alkoxythiazole-2(3H)thiones (stable with respect to daylight). Additionally, the radical liberation process should be initiated by light with a wavelength of around 350 nm. To find promising compounds, 18 test candidates were obtained by a systematic variation of the parent compound N-alkoxythiazole-2(3H)thione. The properties of the test molecules were computed by a protocol that was already successfully used to rationalize the photochemical behavior of N-alkoxypyridine-2(1H)thiones and N-alkoxythiazole-2(3H)thiones. The computations identify two promising new compounds. For N-methoxy-(1,3)dihydro-[1,3]azaphosphole-2-thione (6a), they predict that the fragmentation process will be initiated by an absorption at 348 nm. An analysis of its fragmentation process indicates that the free excess energy of the resulting radicals should more resemble the situation found for N-alkoxypyridine-2(1H)thiones. For N-methoxy-(1,3)dihydro-pyrrole-2-thione (3a), the excitation energy is somewhat higher (330 nm), but the computed fragmentation paths again indicate that the remaining excess energy of the released radicals is quite favorable. The test molecules also contained the experimentally well-known N-methoxypyridine-2(1H)one (1b). For this molecule, our computed data rationalizes nicely the experimental findings.

Alcohols↗

PubMed1994

Cellular and molecular mechanisms in photochemical sensitization: studies on the mechanism of action of psoralens.

The interaction of chemicals and light to induce sensitization reactions in the skin is a complex multistep process resulting in physiological changes in both the dermal and epidermal cell layers as well as characteristic inflammatory reactions. It is becoming increasingly apparent that an array of growth factors and cytokines acting on different components of the skin are involved in the regulation of these processes. One of the best characterized classes of chemical photosensitizers are the psoralens, a group of compounds that must be activated by UV light in wavelengths ranging from 320 to 400 nm (UVA) to initiate their biological actions. Recent evidence suggests that the ability of the psoralens to induce sensitization reactions, which include alterations in epidermal cell growth and differentiation, is highly specific and due to interactions with the epidermal growth factor (EGF) receptor. Specific receptor proteins for the psoralens have been identified in cytoplasmic and membrane fractions of responsive cells. Binding of psoralens to these proteins is of high affinity and reversible. UVA light causes psoralens to photoalkylate their receptors, a process thought to activate the receptor. One early biochemical event at the cell surface membrane linked to psoralen-receptor activation is the inhibition of EGF binding and alterations in the structure and function of the EGF receptor. These findings suggest that the cell surface membrane is an important target for chemical photosensitizers such as the psoralens. In addition, since photoactivated psoralens modulate epidermal cell growth and differentiation, the ability of these compounds to modify the function of the EGF receptor may underlie their biological activity as chemical photosensitizers.

Animals↗