bluuebunny/crossref_metadata_2025 huggingface dataset:
THE ULTRAVIOLET FLUORESCENCE OF BACTERIORHODOPSIN AND THE LOCATION OF TRYPTOPHANYL RESIDUES
Authors: Sherman Warren V.
Published: January 2008

Abstract— The ultraviolet fluorescence spectrum of bacteriorhodopsin is characterized by emission from an ensemble of internal, surface and exposed Trp residues. The temperature dependence of fluorescence yields exhibits a discontinuity at about 30°C coincident with previously observed transitions in membrane lipid microviscosity, photocycle lifetime and photoconductivity. Quenching at high pH coincides with ionization of Tyr and an emission red shift to a spectrum typical of that of tyrosinate. Guanidine hydrochloride produces only partial protein denaturation, increasing the number of exposed Trp by 50%. While exposed Trp in native bacteriorhodopsin are in the minority, they represent a higher proportion of total Trp than is found in rhodopsin of animal rod outer sections.
DARK MEMBRANE LYSIS AND PHOTOSENSITIZATION BY 3‐CARBETHOXYPSORALEN*
Authors: Muller‐Runkel Renate , Grossweiner Leonard I.
Published: January 2008

Abstract— Aqueous solutions of 3‐carbethoxypsoralen (3‐CPs) induce lysis of egg lecithin liposomes and whole human erythrocytes in the dark. Near‐UV irradiation of 3‐CPs sensitizes the inactivation of lysozyme attributed to the production of reactive radical intermediates. The implications of these findings for the use of 3‐CPs as a sensitizer in PUVA therapy of psoriasis are discussed.
THEORY OF THE OPTICAL ABSORPTION OF LIGHT‐ADAPTED BACTERIORHODOPSIN AND ITS ACIDIFIED FORMS
Authors: Yoshihara Toru , Suzuki Hideo , Maeda Akio
Published: January 2008

Abstract— We assume a model for bacteriorhodopsin chromophore such that the protonated retinal Schiff‐base (PRSB) interacts with two anions in the case of light‐adapted bacteriorhodopsin (bRL), while it does with one anion in the case of the acidified form of bacteriorhodopsin (bRacid600). On the basis of this model, the π‐electronic states of all‐trans‐PRSB are calculated according to our LCAO‐ASMO‐SCF‐CI method, the anions being approximated by negative point‐charges in the plane of PRSB π‐system. A possible distribution of the negative point‐charges around PRSB is proposed for the chromophores of bRL, bRacid600, and the two irradiated forms of bRacid600 (the one at 3°C containing 9‐cis‐PRSB, and the other at — 72°C all‐trans‐PRSB). It is shown that the wavelength λmax of absorption maximum observed for each form of bacteriorhodopsin can be explained reasonably well by the suggested charge distribution. Furthermore, a model for the structure of the active site of bRL is proposed, considering that two COO− groups form the anions that interact with PRSB. The calculated optical absorption of all‐trans‐PRSB at such a site is shown to be consistent with the observed absorption spectrum of bRL.
ON THE TWO FORMS OF INTERMEDIATE M OF BACTERIORHODOPSIN
Authors: Ohno Koki , Takeuchi Yasuaki , Yoshida Masasuke
Published: January 2008

Abstract— The decay time course of intermediate M of bacteriorhodopsin was investigated by flash spectrophotometry. The decay was composed of two exponentials showing the existence of two forms of intermediate absorbing around 410 nm. The two were very different in kinetic character whereas the absorption spectra were almost the same. The relative yield of the two components was a function of the intensity of the exciting flash and the slower component disappeared when the flash intensity was made very small. A model based on the trimeric cluster structure of bacteriorhodopsin is proposed.
STEREOELECTRONIC PROPERTIES OF PHOTOSYNTHETIC AND RELATED SYSTEMS—IX. AB INITIO QUANTUM MECHANICAL CHARACTERIZATION OF THE ELECTRONIC STRUCTURE AND SPECTRUM OF THE BACTERIOCHLOROPHYLLIDE a ANION RADICAL
Authors: Petke J. D. , Maggiora Gerald M. , Sipman Lester L. , Christoffersen Ralph E.
Published: January 2008

Abstract— Ab initio configuration interaction wavefunctions and energies are reported for 19 doublet states of the anion radical of ethyl bacteriochlorophyllide a (Et‐BChl a˙), and are employed in a resolution of the electronic absorption spectrum, as well as in a comparison with a previously reported study of the electronic states and spectrum of the anion radical of ethyl bacteriopheophorbide a (Et‐BPheo a˙).

The lowest two excited doublet states, D1 and D2, of Et‐BChl a˙ are found to be approximately degenerate and are predicted to contribute to the experimentally observed absorption at 10000 cm−1. In contrast, the D2←D0 transition in Et‐BPheo a˙ is predicted to contribute to the 11000 cm−1 absorption, while the D1←D0 transition appears at approximately 8600 cm−1 with a low oscillator strength (f= 0.002). The prominent visible absorption at ∼15700 cm−1 in both molecules is found to be due to the D4← D0 transition.

Another difference between the predicted spectra of the two molecules appears in the low‐energy shoulder of the Soret band. Here, two intense transitions, D10←D0 and D11←D0, are predicted for Et‐BChl a˙, as opposed to three fairly intense transitions, D7←D0, D8←D0 and D9←D0, for Et‐BPheo a˙, differences which may provide a means of distinguishing between the two molecules using resonance Raman spectroscopy.

The remainder of the Soret band of Et‐BChl a˙ above 26000 cm−1 consists of a number of closely‐spaced transitions to states D12←D18. The intense transitions D12←D0, D13←D0, D14←D0 are predicted to contribute to the Soret maximum near 30000 cm−1.

The ground state spin densities of the two molecules are similar, with the minor difference of somewhat less spin density located on the methine carbon atoms of Et‐BChl a˙ compared with Et‐BPheo a˙.
CHARACTERIZATION OF THE PHOTOREACTION BETWEEN DNA AND AMINOMETHYL‐TRIMETHYLPSORALEN USING ABSORPTION AND FLUORESCENCE SPECTROSCOPY
Authors: Johnston Brian H. , Hearst John E.
Published: January 2008

–The use of absorption and fluorescence spectroscopy for following the progress of the photo‐reaction between DNA and 4′‐aminomethyl‐4,5′,8‐trimethylpsoralen (AMT) has been investigated. Absorption at long wavelengths and fluorescence both decline upon intercalation of AMT into the DNA helix. The loss of fluorescence from AMT and the accompanying appearance of monoadduct fluorescence upon irradiation by UV light can be easily followed by using the excitation beam of a spectro‐fluorometer as the source of irradiation and monitoring the changing emission spectrum. Where cross‐link formation is possible, the subsequent decline of monoadduct fluorescence is seen as well. This suggests that the 4,5‐tnonoadduct is a precursor of cross‐links. Both monoaddition and cross‐linking are more rapid with poly d(A·T) than with calf thymus DNA or poly d(A·T). Excitation spectra can be helpful in resolving the levels of AMT and 4′,5′‐monoadduct when both are contributing to the emission spectrum. Some changes are observed in the emission spectrum of AMT–poly d(A·T) monoadducts after prolonged irradiation which indicate further photoreaction.
THE ROLES OF THE REL+ GENE AND OF 4‐THIOURIDINE IN KILLING AND PHOTOPROTECTION OF ESCHERICHIA COLI BY NEAR‐ULTRAVIOLET RADIATION*
Authors: Tsai Shung‐Ching , Jagger John
Published: January 2008

Abstract— Photoprotection is a reduction in response to far‐UV (190–300. nm) radiation in cells that have been previously exposed to longer wavelengths. It has been proposed that photoprotection operates by means of a growth delay that permits more time for dark repair. Growth delay in Escherichia coli utilizes 4‐thiouridine (4Srd) in transfer RNA as a chromophore and it requires the rel+ gene, which exerts a stringent control upon RNA synthesis. Mutants that were either rel or 4Srd− were isolated from E. coli B, utilizing a near‐UV‐induced growth‐delay selection technique. The rel mutants, which undergo little growth delay after near‐UV irradiation, show only 50% as much photoprotection as wild types, while 4Srd− mutants show no photoprotection at all. Thus, photoprotection appears to utilize 4Srd as its sole chromophore in E. coli B and B/r, and no more than 50% of photoprotection in these strains can be a result of near‐UV‐induced growth delay.
MECHANISM OF HIGH POWER PICOSECOND LASER UV INACTIVATION OF VIRUSES AND BACTERIAL PLASMIDS
Authors: Gurzadyan G. G. , Nikogosyan D. N. , Kryukov P. G. , Letokhov V. S. , Balmukhanov T. S. , Belogurov A. A. , Zavilgelskij G. B.
Published: January 2008

Abstract— The mechanism of inactivating action of high‐power picosecond laser UV radiation (λ= 266 nm) on the λ and φX174 bacteriophages and the pBR 322 plasmid has been studied. It has been shown that at UV radiation intensities from 1011 to 1013 W/m2, inactivation of viruses and bacterial plasmids occurs mainly on account of single‐strand breaks in the DNA chain unlike the case of less powerful UV radiation where the inactivation is associated with the formation of pyrimidine dimers.
UV‐ENHANCED REACTIVATION OF MINUTE‐VIRUS‐OF‐MICE: STIMULATION OF A LATE STEP IN THE VIRAL LIFE CYCLE
Authors: Rommelaere Jean , Vos Jean‐Michel , Crnelis Jan J. , Ward David C.
Published: January 2008

Abstract— UV‐enhanced reactivation of minute‐virus‐of‐mice (MVM), an autonomous parvovirus, was studied in parasynchronous mouse A9 cells. The survival of UV‐irradiated MVM is increased in cells which have been UV‐irradiated prior to infection. UV‐enhanced reactivation can be explained neither by facilitated plaque detection on UV‐treated indicator cells, nor by altered kinetics of virus production by UV‐irradiated cells. No effect of the multiplicity of infection on virus survival was detected in unirra‐diated or irradiated cells. The magnitude of UV‐enhanced reactivation is a direct exponential function of the UV dose administered to the virus while virus survival is inversely proportional to the UV dosage. The expression of UV‐enhanced reactivation can be activated in cells arrested in G0, it requires de novo protein synthesis and it is maximal when cells are irradiated 30 h before the onset of viral DNA replication. Early phases of the viral cycle, such as adsorption to cellular receptors, migration to the nucleus and uncoating, were not affected by cell irradiation and are unlikely targets of the UV‐enhanced reactivation function(s). These results, together with the single‐strandedness of the viral genome, strongly suggest that the step stimulated in UV‐irradiated cells functions concomitant with, or subsequent to, viral DNA replication.
IMPACT OF UV‐B RADIATION UPON ESTUARINE MICROCOSMS
Authors: Worrest Robert C. , Thomson Bruce E. , Dyke Henry Van
Published: January 2008

Abstract— Twelve flow‐through estuarine microcosms were exposed daily to four different levels of UV‐B radiation (290–320. nm)(1.57 ± 102, 6.43 ± 103, 6.86 ± 103 and 7.61 ± 103 J·m‐2d−1) in addition to a natural level of visible solar radiation (380‐800. nm). The parameters studied over a four week period were phytoplankton community composition, plankton biomass (ash‐free dry weight), chlorophyll a concentration and primary productivity (radiocarbon uptake). With increased exposure to UV‐B radiation there was an obvious alteration of the community composition. Daily exposure to enhanced levels of UV‐B radiation also depressed the biomass, the chlorophyll a concentration and the radiocarbon uptake of samples from the ecosystems.
A MgWO4 PHOTOCONVERTER‐BASED PERSONNEL UV‐B DOSIMETER*
Authors: Davidson G. , Sluder R. B. , Kofsky I. L. , Goldsmith G.
Published: January 2008

Abstract— Design, construction, and testing of a photoelectronic UV‐B personnel dosimeter whose optical system and thus wavelength and angular response match closely the Robertson‐Berger sunburn ultraviolet meter is described. Erythemal irradiance is sensed by a MgWO4 fluor, and cumulative exposure is stored in digital form by custom‐built hybrid microcircuits for readout through a microcomputer at a central station or a field display unit. Sensitivity and exposure storage capacity are designed to provide research‐standard precision in measurements of a few hours to ∼ 2 months duration, and a high level of temperature stability has been achieved. The dosimeter's compactness, rugged and waterproof construction, and wide dynamic range make it applicable to laboratory and environmental photobiology research as well as in skin cancer epidemiology studies.
CHEMILUMINESCENCE FROM CARBENE OXIDATION
Authors: Turro Nicholas J. , Butcher Jared A. , Hefferon George J.
Published: January 2008

Abstract— The chemiluminescent reaction between carbenes and O2 in Freon 113 at and above 77 K was investigated. The reaction was found to be general for phenylated carbenes and independent of precursor. Spectra obtained by optical multichannel analyzer (OMA) are consistent with the emission being from the excited ketone formed. Kinetics studies at 77 K indicate that the decay of the chemi‐luminescence is significantly faster than the decay of the carbene as monitored by fluorescence and electron paramagnetic resonance.
MAMMALIAN CELL VIRAL CAPACITY: AN ALTERNATIVE ASSAY FOR ULTRAVIOLET RADIATION DAMAGE
Authors: Coohill Thomas P.
Published: January 2008

Abstract— A comparison is made between the use of colony forming ability and the capacity of cells to produce viruses following infection (called capacity) as assays for the response of mammalian cells to UV radiation. Experiments using two different types of mammalian cells, a rapidly growing, good colony forming monkey kidney cell line (CV‐1P) and a slowly growing human skin fibroblast line that was a relatively poor and variable colony former (XP25RO), were conducted using both assay systems. Viral capacity was found to be a more consistent indicator of UV damage to cultured cells than was colony forming ability, especially for the XP25RO cells. Apparent advantages and disadvantages of the use of capacity as an indicator of UV radiation damage are discussed.
PHOTOOXIDATION OF CHLOROPHYLL AND PHEOPHYTIN. QUENCHING OF SINGLET OXYGEN AND INFLUENCE OF THE MICELLAR STRUCTURE
Authors: Chauvet Jean‐Paul , Villain Françoise , Viovy Roger
Published: January 2008

Abstract— When chlorophyll(Chl) and pheophytin(Phn) are irradiated in Triton X‐100 water binary solvents, singlet oxygen is formed in the medium in a higher yield for Phn than for Chi. Chlorophyll shows an irreversible photooxidation reaction and a chemical oxidation reaction when 1,3‐diphenyliso‐benzofuran (DPBF) is added to the solution. During the chemical oxidation, Chi is destroyed by an oxidizing agent that is a reaction product of the endoperoxide formed in the medium by the addition of singlet oxygen to DPBF. This reaction depends on the structure of the medium and has some characteristics of an oxidation by hydroxyl radicals. The highest yield is obtained with the micellar structure. Chlorophyll and Phn are readily oxidized by hydroxyl radicals generated using the Fenton reagent. This suggests that in the presence of Triton X‐100, the Mg2+ ion of a Chi molecule plays a key role in the irreversible oxidation of the pigment.
PHYCOERYTHROCYANIN: ITS SPECTROSCOPIC BEHAVIOR AND PROPERTIES
Authors: MacColl Robert , O'Connor Gerald , Crofton Gregory , Csatorday Károly
Published: January 2008

Abstract— Phycoerythrocyanin is a biliprotein found in very few blue‐green algae. Its properties have been examined under three conditions: in whole cells, in light‐harvesting organelles (the phycobilisomes). and as an isolated protein. Absorption and fluorescence bands characteristic of the isolated protein are essentially the same as those in intact cells of the blue‐green alga Anabaena variabilis. The same spectroscopic hallmarks are observed in purified phycobilisomes. Dissociation of these physobilisomes at low‐phosphate concentrations resulted in increased phycoerythrocyanin fluorescence. This time‐dependent increase in fluorescence demonstrates the function of this biliprotein in excitation‐energy transfer to the other biliproteins when the organelles are intact. The relative stabilities of the various heteroprotein bonds within the phycobilisomes are shown to possess differing phosphate ion dependencies. Studies on the isolated protein from Mastigocladus laminosus include fluorescence measurements at both 23 and‐196°C, as is generally observed with biliproteins, although phycoerythrocyanin has complex visible absorption and excitation spectra, only a single emission band is observed.
Rogerio Meneghini
Authors: Menck Carlos F. M.
Published: January 2008

Abstract— Mouse cells (3T3 line) and human fibroblasts are equally sensitive to UV light. At fluences of 2.0–2.5 J/m2 mouse cells excise only 20% of the pyrimidine dimers as compared to 80% excised by human fibroblasts. This fluence allows 37% survival in both cases. Hence, mouse cells are more resistant to the same burden of unexcised dimers. The reason for this increased tolerance to dimers does not seem to be due to a recombinational mechanism, as judged by the fact that only ca. 5% of the dimers are transferred from parental to daughter strands. The transfer of dimers was measured by the Micrococcus luteus UV endonuclease assay, irradiating cells at Gi to avoid artifacts arising from introduction of dimers in nascent strands. The possibility of other mechanisms being involved in the process of tolerance to DNA lesions is discussed.
DETERMINATION OF EXTINCTION COEFFICIENTS OF OAT PHYTOCHROME BY QUANTITATIVE AMINO ACID ANALYSES
Authors: Roux Stanley J. , McEntire Kerry , Brown William E.
Published: January 2008

Abstract— Previously published extinction coefficients for phytochrome were based on indirect colori‐metric estimates of protein weight, mostly by the Lowry method, using bovine serum albumin as a standard. This paper reports revised values based on quantitative amino acid analyses of highly purified phytochrome. The molar extinction coefficient of the red‐absorbing form of phytochrome with 120000mol. wt subunits was found to be approximately 102000cm”1 per 120000moi. wt at 667nm. The molar extinction coefficients at 667 nm for phytochrome with 120000 mol. wt subunits and for the 60000 mol. wt chromopeptide of Pr were found to be approximately the same for samples of equivalent purity. Included in the amino acid analyses of phytochrome with 120000 mol. wt subunits are values for cysteine (11) and cystine (1), measured by two different techniques that gave the same results and agreed well with the estimate of total half‐cystine (14) obtained by an independent method. Tryptophan was quantitated by analysis of a p‐toluene sulfonic acid hydrolysate.
PHOTOTACTIC BEHAVIOR OF INDIVIDUAL CELLS OF CRYPTOMONAS SP. IN RESPONSE TO CONTINUOUS AND INTERMITTENT LIGHT STIMULI
Authors: Watanabe Masakatsu , Furuya Masaki
Published: January 2008

Abstract— The phototactic response of cells of Cryptomonas sp. to stimulation with continuous or intermittent lateral light was determined by an individual cell method using photomicrography and videomicrography. The cells showed positive phototaxis under the conditions studied. The phototactic orientation of individual cells was induced most effectively by irradiation with light of 570 nm; blue light was less effective, and no orientation was found in red light. An intermittent stimulus regime with a long dark interval (250 ms) elicited a weaker phototactic orientation than did a regime with a short dark interval (63 ms) irrespective of the duration of light pulses (16, 250 and 1000 ms). The swimming rate was ca. 240 ums ‐1 and the rotation period ca. 450 ms in the dark, neither of which was greatly affected by stimulation with continuous or intermittent light. Neither step‐up nor step‐down photophobic responses were observed at the time of onset or removal of the light stimulus under the experimental conditions. The swimming direction of individual cells became gradually oriented toward the light source. Phototactic response was detectable within 4 s after the onset of light stimulation, reaching a saturation level after more than 30 s.
BOVINE OCULAR SQUAMOUS CELL CARCINOMA: UV SENSITIVITY IN LYMPHOCYTES
Authors: Lavin Martin F. , Jennings Philip A. , Hughes Darryl J.
Published: January 2008

Abstract— Increased sensitivity to UV light has been demonstrated in Phytohaemagglutinin stimulated lymphocytes from normal and tumour‐bearing Hereford cattle when compared to lymphocytes from other breeds. Trypan blue exclusion and inhibition of DNA synthesis were used to determine cell viability. The results obtained from time course and radiation dose experiments demonstrate biphasic survival kinetics. This is indicative of at least two separate cell populations, exhibiting differentia! sensitivity to UV. The increased sensitivity to UV observed in Herefords may reflect a general sensitivity to UV or alternatively a different cellular constitution in the mitogen stimulated cultures. DNA repair synthesis, measured in the presence of hydroxyurea, was of similar levels in cell cultures from Herefords and one of the control breeds.
EFFECT OF EXPOSURE TO LIGHT ON ENZYME ACTIVITIES and TRYPTOPHAN METABOLITES OF THE KYNURENINE PATHWAY IN WISTAR, IN HETEROZYGOUS and HOMOZYGOUS ADULT and NEWBORN GUNN RATS
Authors: Allegri G. , Costa C. , Antoni A. De , Baccichetti F. , Vanzan S. , Rubaltelli F. F.
Published: January 2008

Abstract— The purpose of this study was to determine the influence of phototherapy used in the treatment of hyperbilirubinemia in infants, on tryptophan metabolism and on enzyme activities involved along the kynurenine pathway in Wistar, icteric homozygous and nonicteric heterozygous Gunn rats after an intraperitoneal loading of 1.0 g/kg body weight L‐tryptophan before and after exposure to visible light. The total mean 24‐h excretion of the tryptophan metabolites in the groups of the Wistar and heterozygous Gunn rats was higher in females than in males and higher than in homozygous groups before phototherapy. Only after exposure to light did the groups of Wistar and heterozygous Gunn rats of both sexes show a decrease in the total excretion of the metabolites. The activities of tryptophan pyrrolase and kynureninase in liver and kynurenine aminotransferase in liver and kidneys were assayed in each group of rats. Male and female Wistar and heterozygous Gunn rats showed a higher activity of tryptophan pyrrolase than the groups of homozygotes in agreement with the data of the metabolites excreted. No difference in enzyme activities was found between the groups of heterozygous and homozygous neonates before and after phototherapy. Phototherapy did not seem to influence these enzyme activities.
AN UNUSUAL PRODUCT OF THE PHOTOCHEMICAL REACTION BETWEEN 6‐METHOXYBENZOFURAN‐ 2,3‐DIONE and STYRENE
Authors: Paknikar S. K. , Kirtany J. K.
Published: January 2008

Abstract— The unidentified product from the photochemical reaction between 6‐methoxybenzofuran‐2,3‐dione and styrene has been assigned a structure based on spectroscopic data and mechanistic considerations.
KINETIC PHOTOCHEMICAL AND PHOTOVOLTAIC ENERGY CONVERSION MODELS
Authors: Landsberg P. T. , Tonge G.
Published: January 2008

Abstract— An energy conversion model descending from, and generalising, models due to BjoUrn, Calvin, Knox. Ross and others has been developed. It uses three sets of levels between which radiative, non‐radiative and storage transitions are possible. Maximisation of the rate of power storage with respect to the absorption threshold yields wavelengths of the order of 680 nm is in good agreement with the absorption peak of chlorophyll a. Departure from the experimental spectra, for example by the substitution of equivalent black‐body spectra, and passage to two sets of levels only, tends to destroy this agreement, which presents chlorophyll a as a materia! optimised through evolution for a maximum rate of power storage in day light. Various meteorological conditions are considered. The results found are not very sensitive to cloud cover. The simplified model for two sets of levels yields an interpretation in terms of transition probabilities of the parameters which occur in the simple solar cell theory. Both types of conversion are thus covered by the same theory. The model is also general enough to deal with photochemical or photovoltaic conversion in undersea conditions.
DIMENSIONAL PROBING OF THE ATP BINDING SITE ON FIREFLY LUCIFERASE
Authors: Rosendahl Mary S. , Leonard Nelson J. , Deluca Marlene
Published: January 2008

Abstract— lin‐Benzoadenosine 5′‐triphosphate has been shown to be an acceptable substrate for light production in the firefly luciferase‐luciferin system. This nucleotide analogue displays strong enzyme binding and a reduced rate of enzyme catalysis compared with ATP. Variation in the color of the bioluminescence emission with /in‐benzo‐ATP compared with ATP suggests that a lateral extension in the purine base induces a change in the conformation of the luciferase and in the environment of the excited light emitter.
COMPARATIVE STUDIES ON THE PHOTOSENSITIZING POTENCY OF 5‐METHOXYPSORALEN and 8‐METHOXYPSORALEN AS MEASURED BY CYTOLYSIS IN PARAMECIUM CAUDATUM AND TETRAHYMENA PYRIFORMIS, AND GROWTH INHIBITION AND SURVIVAL IN CANDIDA ALBICANS
Authors: Young A. R. , Barth J.
Published: January 2008

Abstract— The photosensitizing potencies of 5‐methoxypsoraIen and 8‐methoxypsoralen were investigated using the following biological end‐points for lethality: (i) cytolysis in the protozoans Paramecium caudatum and Tetrahymena pyriformis, (ii) inhibition of growth in the yeast Candida albicans and (iii) survival as measured by colony counts in Candida albicans. In all cases, 5‐methoxypsoralen proved to be the more potent photosensitizing agent. The preliminary action spectra of the 2 compounds for growth inhibition in C. albicans were similar and showed maximal spectral efficiency in the 320–340 nm waveband. The molecular basis for the described end‐points is unknown. Although it is well known that 5‐methoxypsoralen and 8‐methoxypsoralen readily photoreact with DNA, it is considered that photo‐reaction with protein should also be given serious consideration as the possible lethal event. The superior effect of 5‐methoxypsoralen is in accordance with some of the physical and photochemical properties of this molecule, but this result is at variance with other studies in different test systems that have been used to compare the photobiological efficacy of these 2 compounds.
BRANCHING PATHWAYS IN THE PHOTOCYCLE OF BACTERIORHODOPSIN
Authors: Kalisky O. , Ottolenghi M.
Published: January 2008

Abstract— The pulsed laser photolysis of light‐adapted bacteriorhodopsin (BR570) is carried out over the temperature range between 25°C and—92°C in neutral and alkaline water‐glycerol solutions. The results arc indicative of considerable complexity, introduced by two temperature dependent branching reactions associated with the intermediates K610, L550 and M412, of the BR570 photocycle. (a) At relatively low temperatures the primary photoproduct K‐610 equilibrates with a blue‐shifted species, Kp. Both K610 and the new intermediate subsequently decay into another species, K'r, in a process which competes with the formation of L550. Finally, K'p converts very slowly to L550. This branched pathway delays the formation of L550 and thus of M412, without affecting the final yield of either species, (b) A thermal back‐reaction regenerating BR570 takes place at the stage of L550, inhibiting the formation of M412. The reaction which also predominates at low temperatures, is relatively inefficient at high pH when the forward L550→ M412 step is highly catalyzed. It is the superposition of both branching mechanisms, (a) and (b), which accounts for the complex effects of temperature and pH on the photo‐cycle of BR570. Mechanism (b) is accounted for by a molecular scheme in which deprotonation of a tyrosine moiety at the stage of L550 constitutes a prerequisite for deprotonation of the retinal‐lysine schiff‐base as required for forming M412. This scheme appears to be directly related to the proton pump. Mechanism (a) introduces additional complexity in the photocycle at low temperatures but its molecular aspects are still unclear.
THE VACUUM ULTRAVIOLET PHOTOCHEMISTRY OF NUCLEOTIDES
Authors: Dodonova N. Ya. , Kiseleva M. N. , Remisova L. A. , Tsycganenko N. M.
Published: January 2008

Abstract— Photodestruction of nucleotides by vacuum UV (λ < 200 nm) and near UV radiation in thin films has been studied; the products were analyzed by thin‐layer chromatography. Vacuum UV photolysis leads to the rupture of the N‐glycosidic bond with liberation of bases, the quantum yield of the process being about 2 × 10‐4 for guanosine‐5'‐monophosphate. No bases have been found among the products of near UV photolysis.

Vacuum UV irradiation of aqueous solutions of adenosine‐5'‐monophosphate and guanosine‐5'‐monophosphate produces, along with bases, some other fluorescent substances. The identity of photoproducts of vacuum UV photolysis with those of γ‐radiolysis is established. The mechanism of photochemical conversion is discussed.
DIFFERING LEVELS OF EXCISION REPAIR IN HUMAN FETAL DERMIS AND BRAIN CELLS
Authors: Gibson Ruth E. , D'Ambrosio Steven M.
Published: January 2008

Abstract— The levels of DNA excision repair, as measured by unscheduled DNA synthesis (UDS) and the UV‐endonuclease sensitive site assay, were compared in cells derived from human fetal brain and dermal tissues. The level of UDS induced following ultraviolet (UV) irradiation was found to be lower (approx. 60%) in the fetal brain cells than in fetal dermal cells. It was determined, using the UV‐endonuclease sensitive site assay to confirm the UDS observation, that 50% of the dimers induced by UV in fetal dermal cells were repaired in 8h, while only 15% were removed in the fetal brain cells during the same period of time. Even after 24 h, only 44% of the dimers induced by UV in the fetal brain cells were repaired, while 65% were removed in the dermal cells. These data suggest that cultured human fetal brain cells exhibit lower levels of excision repair compared to cultured human fetal dermal cells.
IS PHYTOCHROME INVOLVED IN THE LIGHT‐MEDIATED CAROTENOGENESIS IN FUSARIUM AQUAEDUCTUUM AND NEUROSPORA CRASSA?*
Authors: Schrott E. L. , Huber‐Willer A. , Rau W.
Published: January 2008

Abstract— In the two fungal species (Fusarium and Neurospora) carotenogenesis has been described as a blue light effect. Generally, phytochrome was believed to be absent in fungi. Recently, work was reported suggesting that this might not strictly be the case. Therefore, we very thoroughly tested these two organisms for any red light effect on carotenogenesis. No action of phytochrome was found, either as a ‘low irradiance response’ or a ‘high irradiance response’. Also, no sequential interaction between blue and red light and between UV and red light was observed. Therefore, we conclude that phytochrome is not involved in carotenogenesis in Fusarium and Neurospora.
PHYTOCHROME ACTION IN LIGHT‐GROWN PLANTS. THE CONTROL OF NITRATE REDUCTION AS A MODEL RESPONSE*
Authors: Johnson C. B. , Whitelam G. C.
Published: January 2008

Abstract— Phytochrome control of nitrate reductase activity has been studied in cotyledons and hypocotyls of light‐grown Sinapis alba. Under polychromatic irradiation, an increase in the fluence rate of far‐red light added to a constant source of photosynthetically active radiation causes a decrease in the phytochrome photoequilibrium and, in the hypocotyl, this results in decreased nitrate reductase activity. However, in the cotyledons this difference is only observed transiently. In both organs, enzyme activity is correlated with the level of the far‐red light absorbing form of phytochrome, Pfr. These correlations are not altered when the fluence rate (with respect to phytochrome) is increased, suggesting that the responses are not fluence rate dependent. The results obtained are consistent with the notion that in fully de‐etiolated seedlings, Pft alone controls nitrate reductase activity.
AN INSTRUMENT FOR ACTION SPECTRUM STUDIES IN DERMATOLOGY
Authors: Lamola A. A. , Landon D. O. , Kochevar I. E. , Harber L. C.
Published: January 2008

Abstract— An instrument designed for convenient determination of action spectra for cutaneous photo‐responses in man and experimental animals is described. Light from 450 W Xe lamp is dispersed by a concave holographic grating. The spectrum from 244 to 616 nm is projected as a planar strip (2 times 17 cm) intercepted by a grid with 31 ports. The bandwidth at each port is 12 nm and the size of the port increases from about 4 × 4 mm to 6 × 8 mm from the low to high wavelength limits, respectively. Typical fluence rates in quanta m‐2 s‐1 are 4.0 times 1019 at 298 nm, 16 times 1019 at 394nm and 22 times 1019 at 538 nm. Responses due to delayed erythema in normal skin and to musk ambrette photoallergy and solar urticaria in patients skin have been elicited with this instrument.
MEMBRANE LYSIS IN CHINESE HAMSTER OVARY CELLS TREATED WITH HEMATOPORPHYRIN DERIVATIVE PLUS LIGHT
Authors: Bellnier David A. , Dougherty Thomas J.
Published: January 2008

Abstract Chinese hamster ovary cells in exponential growth were incubated with various concentrations of hematoporphyrin derivative (HpD). Cellular porphyrin content was determined after 2 h incubation at 37°C using [3H]‐hematoporphyrin derivative. Photoactivation of cell‐bound HpD by red light resulted in a family of survival curves with terminal slopes proportional to cellular HpD concentration. The degree of cellular lysis, assayed 1 h after illumination using a chromium‐51 labeling technique, was also found to be related to cellular HpD concentration. The amount of 51Cr released increased with post‐irradiation incubation to a level parallel to cell lethality as measured by colony formation. These data suggest that lysis of the cell membrane may be largely responsible for cellular inactivation following HpD photoirradiation.
ELECTROGENERATED CHEMILUMINESCENCE OF SEVERAL POLYCYCLIC AROMATIC HYDROCARBONS
Authors: Sharifian Hossein A. , Park Su‐Moon
Published: January 2008

Abstract Electrogenerated chemiluminescence (eel) of several polycyclic aromatic hydrocarbons (PAH) (‐)/triphenylamine (TPA) derivative (+) mixed systems has been studied at a platinum wire electrode in acetonitrile (ACN) and tetrahydrofuran (THF) solutions using tetra‐n‐butylammonium perchlorate (TBAP) as a supporting electrolyte, and the results are reported. Exciplexes, as well as the lowest singlet excited state of PAH, are identified as emitting species in these eel systems. The results shown by the temperature and pulse duration dependencies on eel intensities indicate that exciplexes are formed directly from solvent separated ion pairs. The interaction of PAH in their excited states with several donor molecules is discussed based on eel and fluorescence quenching results.
ENERGY TRANSFER IN SELF‐ASSEMBLED CHLOROPHYLL a SYSTEMS *
Authors: Yuen M. J. , Shipmanj L. L. , Katz J. J. , Hindman J. C.
Published: January 2008

Abstract Computer deconvolution of the optical absorption spectra has been used to follow the formation and transformation of various chlorophyll species formed by lowering the temperature in solutions of toluene or methylcyclohexane containing a hydrogen‐bonding nucleophile such as ethanol. At cryogenic temperatures the self‐assembled chlorophyll a‐ethanol species has optical properties similar to those of special pair photoreaction center chlorophyll. Analysis of the absorption and fluorescence behavior of the self‐assembled species suggests that chlorophyll‐chlorophyll species are also formed in the self‐assembly process. Fluorescence lifetime measurements indicate that the pathways for dissipation of excitation energy in these multicomponent systems are complex. Selective optical excitation at wavelengths corresponding to absorption of monomer, oligomer, etc. chlorophyll a species has been used to demonstrate the heterogeneous nature of these self‐assembled systems.
CHEMILUMINESCENCE OF BENZO[a]PYRENE‐7,8‐DIOL *
Authors: Seliger H. H. , Thompson A. , Hamman J. P. , Posner G. H.
Published: January 2008

Abstract The chemiluminescence (CL) of benzo[a]pyrene‐7,8‐diol (BP‐7,8‐diol), originally observed in liver microsomal extracts, has been produced in greater than 104 higher yield by reaction with NaOCl + H2O2. The kinetics and the substrate concentration dependence for the NaOCl/H2O2 initiated CL are the same as those for Rose Bengal photosensitization of CL. In this latter singlet oxygen generating system the CL is quenched by β‐carotene at a diffusion controlled rate of 1.2 × 1010M−1 s−1. The chemically‐initiated CL emission spectrum of BP‐7,8‐diol appears to be the same as that of the microsomal CL. The long lifetime of the CL (τ= 240 s), the production of CL by 1O2 and the effects of electron donors upon the effective rate constant for decay of CL are consistent with the formation of a dioxetane intermediate. The linear dependence of CL upon substrate concentration indicates that the emission is from a monomer excited state rather than from an exciplex as suggested previously. Under the same chemical conditions the relative light yields from benzo[a]pyrene, its 12 monohydroxy derivatives and its other dihydro‐diol derivatives range from 10−2 to 10−5 of the CL from BP‐7,8‐diol. The specificity of the chemically‐initiated CL of BP‐7,8‐diol may provide a sensitive assay for this metabolite.
STEREOELECTRONIC PROPERTIES OF PHOTOSYNTHETIC AND RELATED SYSTEMS. XI. AB INITIO QUANTUM MECHANICAL CHARACTERIZATION OF THE ELECTRONIC STRUCTURE AND SPECTRA OF THE CHLOROPHYLLIDE a AND PHEOPHORBIDE a ANION RADICALS
Authors: Petke J. D. , Maggiora G. M. , Shipman Lester L. , Christoffersen Ralph E.
Published: January 2008

Ab initio configuration interaction wavefunctions and energies are reported for the ground and low‐lying excited doublet states of the anion radicals of ethyl chlorophyllide a (Et‐Chl a‐) and ethyl pheophorbide a (Et‐Pheo a‐), and are employed in a comparative analysis of their respective electronic absorption spectra.

Strong similarities exist between the first five computed excited states of both molecules, providing no distinguishing features in the electronic absorption spectra below 20000 cm‐. Their ground state charge and spin density distributions are also very similar, and there is negligible spin density predicted on the magnesium atom in Et‐Chl a‐.

The Soret bands of both molecules are predicted to arise from intense transitions to several closely‐spaced higher excited states, and the calculations indicate that there are significant differences in the number and composition of these states in the two molecules. It is suggested that these differences may provide a means of distinguishing between the two molecules using resonance Raman spectroscopy.
ANALYSIS OF PHOTOTRANSFORMATION INTERMEDIATES IN THE PATHWAY FROM THE RED‐ABSORBING TO THE FAR‐RED‐ABSORBING FORM OF AVENA PHYTOCHROME BY A MULTICHANNEL TRANSIENT SPECTRUM ANALYZER
Authors: H. Pratt LEE , SMMAZAKIT Yukio , Inoue Yasunori , Furuya Masaki
Published: January 2008

Phototransformation of the red‐absorbing form of phytochrome (Pr) to the far‐red‐absorbing form (Pfr) was followed with a custom‐built transient spectrum analyzer. Large phytochrome, which consisted of approximately 120000‐dalton monomers, was immunopurified or conventionally purified from etiolated oat (Avena sativa L., cv. Garry) shoots. Phototransformation was initiated by exciting Pr with a 115‐mJ, 600‐ns half‐width, 655‐nm laser pulse. Absorption spectra were recorded on a microsecond time scale at predetermined times after the flash. It has been reported earlier that flash excitation of large oat Pr produces a transformation intermediate with maximum absorbance near 700 nm in a difference spectrum and that this intermediate decays by two kinetically distinct reactions. Difference spectra for these two reactions are indistinguishable. Both show bleaching centered at 690 nm with no detectable associated absorbance increase between 570 and 830 nm. Subsequent appearance of absorbance at 724 nm, which presumably but not necessarily represents the appearance of Pfr, had earlier been shown to occur by two kinetically distinct reactions for large oat phytochrome. Data presented here indicate in addition the occurrence of a third, slower reaction. Difference spectra for the two faster reactions are indistinguishable, both with maxima near 728 nm and minima near 650 nm. The difference spectrum for the slowest component, however, was qualitatively different exhibiting a maximum near 722 nm with no corresponding minimum. About 15‐20% of the absorbance increase at 724 nm occurred by this slowest reaction, which exhibited a half‐life of 3 s at 25°C and a Q10 of 1.2 for immunopurified and 1.5 for conventionally purified phytochrome. The percentage occurring by this reaction was independent of temperature over the range studied (1‐25dEC). For immunopurified phytochrome the enthalpy of activation, Gibbs free energy of activation, and entropy of activation of this slowest reaction were found to be about lOkJ‐mol‐1, 75kJ.mol‐1, and ‐220 J.mol‐1 K‐1, respectively, and for conventionally purified phytochrome 25kJ.mol‐1, 75kJ.mol‐1and —170 J.mol‐1 K‐1, respectively. The thermodynamic characteristics of this reaction indicate that it may involve a significant ordering of the protein moiety as it transforms to Pfr.
ON THE ACCURACY OF DIFFERENTIAL MEASUREMENTS OF THE MINIMAL ERYTHEMA DOSE: INFLUENCE OF THE DISCRETENESS OF THE SCALE
Authors: Bruls WielA. G. , Faber Joop A. J. , Leun Jan C. van der
Published: January 2008

The minimal erythema dose (MED) is often used as a quantity by which the influence of certain treatments of the skin can be measured. Differential measurements are performed by assessing the difference of the MED on the skin treated in some way and the untreated skin.

As the MED‐measuring scale is discrete, the question is sometimes raised whether it is possible to measure differences smaller than one scale unit. In the present paper it is shown that this is indeed possible; in principle the discreteness of the scale does not impose any restriction on the smallest value of the difference that can be measured. The discreteness of the scale introduces an extra random variation into the measurement. This variation is estimated theoretically. It is automatically included in the usual error analysis.

The discreteness variance is small when compared to other variance components, which are computed from an analysis of variance of actual experiments. Reducing the discreteness variance, by reducing the dose decrement of the MED‐measuring scale, therefore, does not enhance the overall accuracy considerably. Finally, it is found that the assessments of the MED by the various observers do not differ significantly from each other, and that multiple assessments do increase the accuracy, especially for small effects.
EFFECTS OF K+ AND Ca2+ IONS ON MOTILITY AND PHOTOSENSORY RESPONSES OF STENTOR COERULEUS
Authors: Colombetti Giuliano , Lenci Francesco , Song Pill‐Soon
Published: January 2008

Extracellular K+ ions above a critical concentration induce ciliary reversal in unstimulated Stentor coeruleus and suppress step‐up photophobic response. This threshold concentration of K+ ions depends on the extracellular Ca2+ concentration, and the subsequent backward gyration and light‐sensitivity suppression seem to depend on the relative concentrations of K+ and Ca2+. The concentration of Ca2+ necessary to overcome K+‐mediated inhibition of phobic response and backward swimming increases non‐linearly with increasing K+ concentration. The Ca2+‐blocking agent. D‐600, selectively inhibits photophobic responses of Stentor, thus further confirming the role of Ca2+ ions in photosensory transduction of this ciliate.
SENSITIZATION BY LUMAZINE PROTEINS OF THE BIOLUMINESCENCE EMISSION FROM THE REACTION OF BACTERIAL LUCIFERASES
Authors: Lee John
Published: January 2008

Abstract— Lumazine protein from Photobacterium phosphoreurn blue shifts the in vitro bioluminescence spectra in the reactions using each of the 4 main types of bacterial luciferases: P. phosphoreum, P. leiognathi, Vibrio harveyi and V. fischeri. For the reaction initiated with FMNH2 and tetradecanal at 2°C, this “sensitizing” property of lumazine protein differs quantitatively between the luciferases. An interaction constant characterizing each type of luciferase may be derived from a reciprocal plot of the spectral shift against the lurnazine protein concentration. The weakest interaction constant is in the V. fischeri reaction, 180 μM. For the V. harveyi reaction the interaction is in the range 6–9 μM, and for both Photobacterium reactions it is 2–3 μM. A concentration of only 0.6 μM of lumazine protein is sufficient to cause an observable change in the Photobacterium bioluminescence spectra. For the V. harveyi case the interaction constant is near to the equilibrium Kd for the luciferase‐lumazine protein complex, observed directly by Visser and Lee. Both constants are decreased markedly by increase in phosphate concentration so that it is concluded that, with V. harveyi luciferase, sensitization occurs within this protein‐protein complex. For P. phosphoreum luciferase, however, the equilibrium complex is too weak to correspond to the sensitizing interaction and it is concluded that the rate‐limiting process is a protein‐protein bimolecular collision. As judged from their molecular weight around 20000, spectral properties, and ability to blue shift the bioluminescence spectra, lumazine proteins are identified in a second strain of P. phosphoreum and in P. leiognathi.
UV‐INDUCED ELEVATION OF SKIN GLYCOSAMINOGLYCAN LEVELS I: RAPID MEASUREMENT OF SKIN GLYCOSAMINOGLYCANS BY TITRATION WITH ACRIDINE ORANGE*
Authors: Menter Julian M. , Pearl William S. , Yadven Mitchell W. , Willis Isaac
Published: January 2008

Abstract— We have developed a simple, rapid, sensitive procedure for measuring polyanionic glycosaminoglycans (GAG) in unfixed defatted lyophilizedSK–1 hairless mouse skin by means of quantitative measurement of uptake of the fluorescent dye acridine orange (AO), which was shown to be GAG‐specific under the conditions of these experiments. This method is suitable for detecting and estimating elevations in steady skin GAG levels due to UV irradiation.
EVALUATION OF DNA CROSSLINKS AND MONOADDUCTS IN MOUSE EMBRYO FIBROBLASTS AFTER TREATMENT WITH MONO‐AND BIFUNCTIONAL FUROCOUMARINS AND 365 nm (UVA) IRRADIATION. POSSIBLE RELATIONSHIP TO CARCINOGENICITY
Authors: Szafarz David , Zajdela François , Bornecque Claude , Barat Nicole
Published: January 2008

Abstract— Formation of crosslinks in DNA by various mono‐ and bifunctional furocoumarins plus UVA light in mouse embryo fibroblasts was evaluated by a NaI density gradient centrifugation method. Angelicin and 3‐carbethoxypsoralen did not form any crosslinks: however, angelicin was slightly carcinogenic for mouse skin, whereas 3‐carbethoxypsoralen was not carcinogenic. Psoralen induced DNA crosslinking, in a dose‐dependent fashion and was highly carcinogenic for mouse skin. In contrast to the psoralen‐induced photoadducts (120 per 106 nucleotides) which were left unrepaired, 41% of the 3‐carbethoxypsoralen adducts (30 per 106 nucleotides) were removed during 1 h of dark post‐incubation.