bluuebunny/crossref_metadata_2025_split huggingface dataset:
BIOCHEMICAL STEPS IN VISUAL TRANSDUCTION: ROLES FOR NUCLEOTIDES AND CALCIUM IONS*
Authors: Bownds M. Deric 
Published: January 2008

Abstract— Recent studies from this laboratory permit the suggestion of a scheme for describing molecular mechanisms which may regulate excitation and adaptation in amphibian rod photoreceptor cells. The experiments have studied several chemical changes which occur upon illumination of isolated rod outer segments: (1) activation of cyclic GMP phosphodiesterase which is sensitive to calcium concentration, (2) a resulting rapid drop in cyclic GMP levels which has stoichiometry and time course appropriate for the internal transmitter presumed to mediate between photon absorption in the disc membrane system and the permeability decrease in the plasma membrane, (3) a dephosphorylation of two small proteins whose phosphorylation is controlled by cyclic GMP levels, and (4) a slower hydrolysis of GTP which may drive efflux of calcium from the outer segment.It is suggested that the rapid decrease in sodium conductance which follows illumination is caused by the dephosphorylation of the two small proteins, with their dephosphorylation being controlled by the cyclic GMP decrease. In a slower reaction light activates a GTP‐dependent extrusion of calcium from the cytoplasmic space. This lowering of internal calcium causes desensitization of the light‐sensitive phosphodiesterase enzyme responsible for the cyclic GMP decrease, so that its intensity‐response function now resembles that of the light‐adapted rod photoreceptor. Thus, changes in plasma membrane conductance are regulated by cyclic GMP, and the sensitivity of the system is controlled by slower calcium movements which set the light‐sensitivity of the phosphodiesterase enzyme. Finally, the light‐initiated phosphorylation of rhodopsin also appears to play a role, with phosphorylated rhodopsin causing desensitization of the phosphodiesterase enzyme.
SPECTROSCOPIC STUDIES OF CUTANEOUS PHOTOSENSITIZING AGENTS—I. SPIN TRAPPING OF PHOTOLYSIS PRODUCTS FROM SULFANILAMIDE, 4‐AMINOBENZOIC ACID AND RELATED COMPOUNDS
Authors: Chignell Colin F. , Kalyanaraman B. , Mason Ronald P. , Sik Robert H. 
Published: January 2008

Abstract—The photodecomposition of sulfanilamide, 4‐aminobenzoic acid and other related analogs has been studied with the aid of the spin trap 2‐methyl‐2‐nitrosopropane. UV photolysis of an aqueous solution of sulfanilamide yielded the following radicals C˙6H4SO2NH2, C6H5SO2˙, S˙O2NH2 and SO‐#˙ (or SO‐2dot;). Under the same conditions 4‐aminobenzoic acid gave C˙6H4COOH. In addition both sulfanilamide and 4‐aminobenzoic acid, but not 4‐dimethylaminobenzoic acid, generated e‐aq or hydrogen atoms during UV irradiation. The C6H4SO2NH2 radical was also produced by photolysis of 4‐iodobenzenesul‐fonamide and 4‐nitrobenzenesulfonamide. The C6H4COOH radical was generated by photolysis of 4‐nitrobenzoic acid and 4‐iodobenzoic acid. Finally the C6H4NO2 radical was formed during the irradiation of 4‐nitroaniline, 1,4‐dinitrobenzene and 4‐iodonitrobenzene. The free radicals generated by sulfanilamide and 4‐aminobenzoic acid may play an important role in the phototoxic and photoallergic responses elicited by these drugs in certain individuals.
1,4‐DIPHENYLBUTADIYNE, A NEW NON‐PHOTODYNAMIC PHOTOTOXIC COMPOUND
Authors: Kagan Jacques , Gabriel Robert , Singh Shiv P. 
Published: January 2008

Abstract—1,4‐Diphenylbutadiyne (DPB), the first member of a new chemical class of phototoxic compounds, was found to be active against E. coli (strain B) under nitrogen but not in the presence of air. It was also phototoxic against both Candida utilis and Saccharomyces cerevisiae aerobically, and against the latter anerobically. The maximum activity against C. utilis occurred at 360 nm, and the uv light was definitely required in the phototoxic act. Circular dichroism spectroscopy disclosed that DPB underwent photoreaction with DNA. This technique, as well as melting temperature profiles, hyperchromicity studies, and the elution profile from hydroxyapatite chromatography indicated that no cross‐linking to double strands had occurred, and that DPB behaved as a monofunctional reagent, interacting only with single strands of DNA photochemically. Finally, 2,5‐diphenylthiophene was synthesized from DPB but was not phototoxic.
FLUORESCENCE OF TRYPTOPHAN IN KERATIN
Authors: Smith Gerald J. , Thorpe Michael R. , Melhuish W. Hugh , Beddard Godfrey S. 
Published: January 2008

Abstract—The excitation and emission spectra have been determined for the fluorescence from trypto‐phan residues in dry keratin. The fluorescence decay was also measured and shown to be a single exponential with a rather long lifetime of 6.9 ns. It is suggested that the emission takes place from a state formed by interaction between the 1La state of the tryptophan residues and neighbouring polar or polarizable groups in the protein.The fluorescence excitation spectrum displays a peak at 290 nm, and its appearance at this position rather than at 280 nm, which is the absorption maximum of tryptophan, is believed to arise from inner filtering by the tyrosine residues in keratin.
LIGHT‐INDUCED FORMATION OF O‐2˙ OXYGEN RADICALS IN SYSTEMS CONTAINING CHLOROPHYLL
Authors: VAN Ginkel Gijsbert , Raison John K. 
Published: January 2008

Abstract—It has been shown recently that photosystem 1 particles, photosystem 1 lipid vesicles and chlorophyll‐a lipid vesicles show identical photochemical reactions in the presence of oxygen e.g. H+‐and O2‐uptake (Van Ginkel, 1979). Therefore, spin‐trapping experiments were done to identify the oxygen radicals formed. The spintrap phenyltertiarybutylnitrone (PBN) failed to yield information about oxygen radicals.With the spintrap 5,5‐dimethyl‐1‐pyrroline‐1‐oxide (DMPO), however, we obtained a mixed spectrum of O‐2˙ and OH·‐adducts generated in chloroplasts, photosystem 1 particles or chlorophyll‐a lipid vesicles. These data indicate that chlorophyll‐a in an artificial membrane can also catalyze O‐2˙‐formation. Chlorophyll‐a lipid vesicles catalyze light‐induced formation of the Tiron‐semiquinone free radical, which has been proposed as a specific O‐2˙‐probe (Greenstock and Miller, 1975). However, OH· scavengers strongly reduce the formation of this radical, whereas superoxide dismutase does not.Pulse‐radiolysis measurements showed that the rate constant for the reaction of Tiron with OH· is 8.2 · 109M‐1 s‐1, which is considerably higher than the published Tiron/O‐2˙ rate constants. Therefore, Tiron is a better spin probe for OH· than for O‐2˙.We suggest that light‐induced H+‐and O‐2˙‐uptake in membranes containing chlorophyll‐a in the presence of ascorbate is caused mainly by the very rapid reaction of OH· with ascorbate.
CARBON‐13 NUCLEAR MAGNETIC RESONANCE STUDIES ON 13C‐ENRICHED RETINALS EMBEDDED IN BACTERIORHODOPSIN
Authors: Yamaguchi Akihito , Unemoto Tsutomu , Ikegami Akira 
Published: January 2008

Abstract— Both [15‐13C] and [14‐13C] all‐trans‐retinals were synthesized. Bacteriorhodopsin containing [14‐13C]retinal as a chromophore, when solubilized with octyl‐β‐D‐glucoside, showed characteristic resonances at 125 and 118 ppm from tetramethyl silane. The former was assigned to the signal from free retinal and the latter from protonated Sehiff base. When the bacteriorhodopsin was denatured in sodium dodecyl sulfate, the signal at 118 ppm disappeared, while the signal at 125 ppm rather increased.In the case of bacteriorhodopsin containing [15‐13C]retinal, when solubilized with Triton X‐100, a characteristic resonance at 169 ppm was distinguishable as a shoulder peak superimposed on the broad signal of carbonyl carbons and it was assigned to the signal from the protonated Sehiff base. The other signal observed at 191 ppm was from free retinal.These results suggested that the Sehiff base of bacteriorhodopsin is protonated in the dark.
PHOTOCHEMICAL REACTION OF 13‐CIS‐BACTERIORHODOPSIN STUDIED BY LOW TEMPERATURE SPECTROPHOTOMETRY
Authors: Iwasa Tatsuo , Tokunaga Fumio , Yoshizawa Tǒru 
Published: January 2008

Abstract— The photoreaction cycle of 13‐cis‐bacteriorhodopsin (13‐cis‐bR) was investigated by low temperature spectrophotometry using two different preparations; 13‐cis‐bR constituted from bacterioopsin and 13‐cis‐retinal, and dark‐adapted bacteriorhodopsin (bRD), which is an equi‐molar mixture of 13‐cis‐bR and trans‐bR.By irradiation with 500 nm light at — 190°C, 13‐cis‐bR was converted to its batho‐product, batho‐13‐cis‐bR (batho‐bR13), which is different from batho‐product from trans‐bR, batho‐bRt. On warming batho‐bR13 to ‐5°C in the dark, it completely changed to trans‐bR. We estimated the composition of 13‐cis‐bR and trans‐bR in the warmed sample spectrophotometrically and then the absorption spectrum of batho‐bR13 was calculated. The absorption maximum lies at 608 nm, 1250 cm−1 longer than that of 13‐cis‐bR; the molar extinction coefficient (ε) is about 74000 M−1 cm−1, larger than that of 13‐cis‐bR (52000 M−1 cm−1).On the warming the sample containing batho‐bR13 formed by irradiating 13‐cis‐bR or bRD at — 190°C, we could not detect other intermediates such as the lumi‐ or meta‐intermediates seen in trans‐bR system.
THE WHITE MEMBRANE OF CRYSTALLINE BACTERIOOPSIN IN HALOBACTERIUM HALOBIUM STRAIN R1mW AND ITS CONVERSION INTO PURPLE MEMBRANE BY EXOGENOUS RETINAL
Authors: Mukohata Yasuo , Sugiyama Yasuo , Kaji Yoshio , Usukura Jiro , Yamada Eichi 
Published: January 2008

Abstract— A new strain isolated from Halobacterium halobium designated R1mW, contained negligible amounts of isoprenoid pigments, had a yellowish white color due to respiratory pigments and showed no proton movement in response to light. However, addition of all‐trans‐retinal converted R1mW into purple cells. Formation of both halorhodopsin and bacteriorhodopsin was indicated by induction of light‐dependent proton uptake and release, respectively. Both haloopsin and bacterioopsin were thus postulated to be present in R1mW. Electron micrographs of freeze‐fractured cytoplasmic membranes revealed patches in a hexagonal array of trimeric particles, comparable to the purple membrane structure.These white membrane patches were isolated by procedures similar to those for the purple membrane. The white membrane's buoyant density was about 1.18 g/m/, and its main component migrated on sodium dodecylsulfate polyacrylamide gels at the same rate as bacteriorhodopsin. The white membrane showed only a small absorption peak at ∼410nm due to contaminating respiratory pigments and a strong absorption at around 275 nm and shorter wavelengths. The white membrane was thus considered to be mainly composed of bacterioopsin, which was readily converted into bacteriorhodopsin by an addition of all‐trans‐retinal.The absorption and CD spectra of the white membrane were measured before and after addition of retinal. The molar extinction coefficient of dark‐adapted bacteriorhodopsin formed was determined to be 53000M−1 cm−1 at 560 nm from retinal binding studies. The CD spectrum of the white membrane was negligible in the visible region but showed several bands assigned to aromatic and backbone structures in the UV region. Retinal addition caused considerable changes in the spectrum, yielding the CD spectrum of crystalline purple membrane bacteriorhodopsin. The white membrane thus appears to be a preparation suitable for structure‐function studies of bacteriorhodopsin.
CIS‐TRANS PHOTOISOMERIZATION OF ABSCISIC ACID
Authors: Brabham Dale E. , Biggs R. H. 
Published: January 2008

Abstract— An important regulator of numerous physiological processes in higher plants is abscisic acid (ABA), which is photoisomerized from the more biologically active cis isomer to the nearly inactive trans isomer by natural sunlight. It is possible that this photoisomerization is a UV control mechanism in functions regulated by ABA.The quantum yields of both the cis to trans and trans to cis photoisomerizations were measured by an initial velocities method under various conditions of pH and oxygen concentration at room temperature. The yield for photoisomerization of cis‐ABA ranged from 0.25 at pH 3.0 to 0.11 at pH 7.0. Oxygen partially quenched the process. The quantum yield varies only slightly with wavelength.The quantum yield of photolysis of cis‐ABA is reported for pH 3.0 as 0.06. This yield also varies slightly with wavelength and is relatively insensitive to oxygen. This relatively high yield explains the loss of potency of ABA during UV irradiation.Phosphorescence of cis‐ and trans‐ABA is observed in methanol at 77 K. Onset of the emission is at 350 nm. The emission spectra is the same for both isomers.From these results a mechanism of UV action on plants based on the photoisomerization of the inactive trans‐ABA to the biologically active cis isomer is proposed.
BLOCKAGE OF RESTRICTION ENDONUCLEASE CLEAVAGE BY THYMINE DIMERS
Authors: Hall Robert K. , Larcom L. L. 
Published: January 2008

AbstractViral DNAs were subjected to 254 nm irradiation and then digested with type II restriction endonucleases. At the fluences used, irradiation inhibited cleavage by nucleases which recognize sites containing neighboring thymines. Cleavage by endonucleases with other recognition sequences was not affected. In viral and plasmid DNAs, this effect could be used to study thymine dimer formation at a few specific, mapped sites of defined base sequence.
FLUORESCENCE LIFETIMES OF CHLOROPHYLL a: SOLVENT, CONCENTRATION AND OXYGEN DEPENDENCE
Authors: Connolly John S. , Janzen A. Frederick , Samuel Edward B. 
Published: January 2008

AbstractFluorescence lifetimes (τf) of chlorophyll a (Chi a) have been measured by the single‐photon‐counting technique over a wide range of concentrations (˜10‐7˜10‐4M) in deoxygenated pyridine, diethyl ether, toluene and methanol. At pigment concentrations ˜1 μM, reabsorption of fluorescence induces significant artifacts on measured values of τf which are dependent on detection wavelength and the specific geometry of the experiment. There is a clear dependence of τf on the nature and degree of solvation, including both coordination of the central magnesium and hydrogen‐bonding of the solvent (viz. alcohols) to the macrocycle. Quenching of the excited singlet state by molecular oxygen was measured quantitatively in ether, and a bimolecular rate constant markedly slower than the diffusion‐controlled limit was obtained.
MICROSPECTROFLUOROMETRIC APPROACH TO THE STUDY OF FREE/BOUND NAD(P)H RATIO AS METABOLIC INDICATOR IN VARIOUS CELL TYPES
Authors: Salmon Jean‐Marie , Kohen Elli , VIALLET Pierre , Hirschberg Joseph G. , Wouters Alain W. , Kohen Cahide , THORELL Bo 
Published: January 2008

AbstractUnder excitation at 365 nm, the cell fluorescence is mainly due to bound and free NAD(P)H, plus a small contribution from flavins. Resolution is first attempted in the simplest case. i.e. the increase spectrum (δIf) due to microinjection of glucose‐6‐phosphate (G6P) into EL2 ascites cells. Above 510 nm, δIF is identical to the spectrum of free NADH. Below 510 nm. the presence of a second component is suggested, i.e. the intensity of the free NADH spectrum is lower than the measured δIF level. The difference between δIf and the free NADH spectrum (maximum at 475 nm) yields a spectrum suggestive of bound NADH with maximum at 450 nm. Thus, with free and bound NADH, the entire δIF can be reconstructed, with some assumptions as to the relative quantum yields of the two components. This seems to leave no place for a flavin component.The questions raised by the lack of such a component are answered using a new microspectrofluorometer, which aiiows correlated monitoring of NAD(P)H and flavins with excitations at 365 and 436 nm, respectively. As detected by excitation at 436 nm, injections of G6P, malate, ADP, and treatments with azide, cyanide or partial anaerobiosis, all indeed show a redox change of flavins, in the sense of decreased emission. It is understandable, however, that such a change which is not very large even using 436 nm excitation should remain undetected when flavins are excited at 365 nm, i.e. using the tail of their excitation spectrum.In contrast to the increased δIF spectrum recorded in response to injected substrate, the initial spectrum (If) of the cell prior to a metabolic perturbation reveals a third component, even with 365 nm excitation. The position and reactivity of this component shows flavin‐like properties. The structural resolution attainable makes it possible to obtain the evaluation of free vs. bound NAD(P)H and flavin fluorochromes in the mitochondrial and cytosolic compartments of the intact cell.
PREBIOTIC FORMATION OF HIGHER MOLECULAR WEIGHT COMPOUNDS FROM THE PHOTOLYSIS OF AQUEOUS ACETIC ACID
Authors: Mendoza Alicia Negrón , Ponnamperuma Cyril 
Published: January 2008

AbstractIn the study of chemical evolution, experiments simulating primitive earth conditions have shown that many compounds of biological significance can be produced from simple precursors. In an attempt to search for the origin of polycarboxylic acids, the UV irradiation of aqueous acetic acid was performed. Among the products detected were succinic, citric and malonic acids which are key compounds in metabolic pathways, suggesting that these compounds might have been formed on the primitive Earth prior to life itself.
THE USE OF DIFFUSERS IN THE MEASUREMENT OF TRANSMISSION OF HUMAN EPIDERMAL LAYERS
Authors: Bruls Wel A. G. , van der Leun Jan C. 
Published: January 2008

Abstract— The transmission of the outermost layers of human skin is measured, by use of a diffuser. The sample is transferred to the diffuser and inserted into the measuring beam. The reference beam is also measured after passing through the diffuser. The diffuser transforms the light in both the sample and reference beams into a completely diffuse flux. The radiant flux of light emerging from the diffuser is directly proportional to the radiant flux of the light impinging on the diffuser, but does not depend on the angular distribution of the impinging light. Because of this particular property, a diffuser may be used to measure the transmission of scattering specimens. The analogy between a diffuser and an integrating sphere is pointed out.Deviations of commercially available diffusers from the perfect behaviour lead to deviations in the measured transmissions that are negligible (< 3%) for epidermal and corneal samples. Spectral transmission data from representative skin samples are presented. It is found that correction for fluorescence is necessary. Due to this correction the epidermal UV‐C transmission is lower by a factor of 10–100 than without correction, and the epidermal absorption maximum is shifted from 275 towards 265 nm.
SUBSTITUTION OF RETINAL BY ANALOGUES IN RETINAL PIGMENTS OFHALOBACTERIUM HALOBIUM.CONTRIBUTION OF BACTERIORHODOPSIN AND HALORHODOPSIN TO PHOTOSENSORY ACTIVITY
Authors: Schimz A. , Sperling W. , Ermann P. , Bestmann H. J. , Hildebrand E. 
Published: January 2008

Abstract—InHalobacrerium hnlobium.retinal is the chromophore of the light‐energy converting pigments bacteriorhodopsin (BR) and halorhodopsin (HR) and of the sensory photosystems. PS 370 and PS 565. In both photosystems as well as in BR and HR. retinal was substituted by retinal analogues.Retinal2(3,4‐dehydro‐retinal).shifts the main sensitivity maximum of PS 370 and of PS 565 by about 1.5 nm to longer wavelengths. The absorption maxima of BR and HR are both shifted in the same direction, but by 37 nm.13‐Ethylretinaland13‐propylretirnalshift the main sensitivity maximum of each sensory photosystem to shorter wavclengths; the absorption maxima of BR and HR are shifted in the same direction but to a smaller extent. Both sensory photosystems are equally active with retinal and with each of the three analogues as the chromophore. After substitution of retinal by the analogues, the action spectra of PS 565 of the BR‐containing strain R1L3show a secondary bensitivity peak in addition to the main peak. This secondary peak matches the absorption maximum of the corresponding BR. In the action spectra of the BR‐deficient strainET–15 this secondary peak is missing. Action spectra of PS 565 of the BR‐deficient strainL–33, which synthesizes increased amounts of HR. with all retinals show a secondary peak which matches the absorption maximum of the corresponding HR.The results show that the analogues can substitute retinal in both sensory pigments as well as in BR and HR. Moreover, the data support the previous assumption that both BRand HR, although not required for photosensory activity can contribute to photosensing through PS 565.
SPECTROSCOPIC STUDIES OF CUTANEOUS PHOTOSENSITIZING AGENTS—VI. IDENTIFICATION OF THE FREE RADICALS GENERATED DURING THE PHOTOLYSIS OF MUSK AMBRETTE, MUSK XYLENE AND MUSK KETONE
Authors: Motten Ann G. , Chignell Colin F. , Mason Ronald P. 
Published: January 2008

Abstract—Musk ambrette (4‐tert‐butyl‐3‐methoxy‐2,5‐dinitrotoluene), a common component of perfumes, soaps, and some food flavorings, can cause cutaneous photosensitization reactions including photoallergy. These may be mediated through free radicals formed during photolysis. When musk ambrette was photolyzed under nitrogen in basic methanol, two distinct nitro anion radicals were identified by electron spin resonance. One radical was centered on a nitro group in the plane of the aromatic ring, while the other was centered on a nitro group twisted out of the plane of the ring due to steric hindrance by bulky substituents on either side of the group: the two radicals appeared to interconvert and maintain an equilibrium concentration ratio. Two closely related compounds which are also used in perfumes, but have not been reported to cause photosensitizing reactions, also produced free radicals during photolysis. Musk xylene (2,4,6‐trinitro‐1,3‐dimethyl‐5‐tert‐butylbenzene) generated two nitro anion radicals, both of which were centered on twisted nitro groups, while musk ketone (3,5‐dinitro‐2,6‐dimethyl‐4‐tert‐butylacetophenone) produced only one nitro anion radical, which is also twisted. Athough these nitro anion radicals are probably the first step in the photolysis of these nitroarornatic molecules, it seems likely that in vivo they will undergo further reduction to produce more reactive species including the corresponding nitroso and hydroxylamine derivatives. In addition, autoxidation of the nitro anion radical intermediate forms superoxide.
DETERMINATION OF THE BINDING CONSTANT OF H14 CO−3 TO THE PHOTOSYSTEM II COMPLEX IN MAIZE CHLOROPLASTS: EFFECTS OF INHIBITORS AND LIGHT
Authors: Stemler Alan , Murphy Judith 
Published: January 2008

Abstract—The binding (dissociation) constant for HCO−3 to the photosystem II complex in maize chloroplasts is approximately 80 μM. One HCO−3 binds per 500–600 chlorophyll molecules. In the dark, formate is a competitive inhibitor of HCO−3 binding, while 3‐(3′,4′‐dichlorophenyl)‐1, 1‐dimethylurea (DCMU) inhibits HCO−3 binding non‐competitively. Light decreases HCO−3 binding in the presence of formate. Light increases the binding of HCO−3 in the presence of DCMU. The high binding constant for HCO, discriminates strongly among the various hypotheses attempting to explain the “bicarbonate‐effect” on photosystem II. The proposal by Stemler and Jursinic (Arch. Biochem. Biophys. 221, 227–237 1983), that HCO−3 is one of a class of monovalent anionic inhibitors of photosystem II, is favored. These anions compete for a specific binding site on the photosystem II complex.