bluuebunny/crossref_metadata_2025 huggingface dataset:
EFFECTS OF INORGANIC NITROGEN ON THE RESPONSE OF LEMNA CARBON DIOXIDE OUTPUT TO LIGHT QUALITY AND TIMING*
Authors: Hillman William S.
Published: January 2008

Abstract—The effects of various light/dark schedules on the time course of CO2 output by axenic cultures of the short‐day plant Lemna perpusilla 6746 differ substantially depending on whether the medium is N‐less or contains NH4 or NO3 as the sole N source. The steady‐state pattern achieved with a daily 1/4 h light pulse in N‐less medium is essentially the same whether the light is red or far‐red; on NO3 or NH4, however, the red and far‐red patterns differ in form and suggest the action of a ‘Pfr‐hourglass’ timer. In darkness, following either continuous light or entrainment to kh red light daily, CO2 output oscillates for three or more circadian cycles on NH4 medium and for at least two on N‐less, but damps after a single cycle on NO3. A schedule of 1/4 h red light every 12 h elicits a 24 h periodicity on NO3 or NH4 media and a 12 h periodicity on N‐less medium, while a similar far‐red schedule elicits a 12 h periodicity on all three. CO2 output patterns on each of the media respond differently to varying the daily span of light from 1/4 to 6 to 12 h. These results are probably due to differential effects of changing N status on the proportion of total C O2 arising from various metabolic reactions. They suggest that, rather than being a simple, unitary indicator, CO2 output can be made to reflect different processes on different media, increasing its value as a real‐time indicator of events underlying photoperiodism.
PHYTOCHROME‐MEDIATED CONTROL OF PROLAMELLAR BODY REORGANIZATION AND PLASTID SIZE IN MUSTARD COTYLEDONS
Authors: Kasemir H. , Bergfeld R. , Mohr H.
Published: January 2008

Abstract— The development of plastids in the palisade parenchyma cells of the cotyledons of mustard seedlings (Sinapis alba L.) was studied by electron microscopy. In darkness the etioplasts undergo a sequence of morphogenic changes previously recognized in principle in bean and barley leaves, as summarized by Rosinski, J. and W. G. Rosen (1972) Quart. Rev. Biol.47, 160–190. From 12 to 36 h after sowing, an increase in the percentage of etioplast profiles with paracrystalline prolamellar bodies can be observed. Thereafter, the degree of organization and size of the prolamellar bodies decrease. 60 h after sowing, the etioplasts show only remnants of prolamellar bodies with irregularly spaced tubules. Continuous far‐red light, which is considered to operate via phytochrome, counteracts the decay of organization of the prolamellar body and strongly increases the size of the plastids. The effect of continuous far‐red light (onset of light 36 h after sowing) can be substituted by 12 h of far‐red light given between 36 and 48 h after sowing. It is shown with red and far‐red light pulses that the morphogenic effect of long‐term far‐red light on plastid size and appearance of the prolamellar body is exclusively due to phytochrome (Pfr). Changes by light in the amounts of protochlorophyll(ide) or chlorophyll(ide) do not affect these results. The action of Pfr on the structure of the prolamellar body is a relatively fast process, occurring within 3 h. Formation of thylakoids does not seem to be under phytochrome control. Rather, this response seems to be related to the protochlorophyll(ide)→ chlorophyll(ide) a transformation.
TIME COURSE OF MICROSECOND DELAYED LIGHT EMISSION FROM SCENEDESMUS OBUQUUS AT INTERMITTENT ILLUMINATION
Authors: Holzapfel Chr. , Haug A.
Published: January 2008

Abstract— For dark adapted cells, the intensity of delayed light at the onset of a light period depends on the length of the preceding dark period. Under our experimental conditions, the exciting laser light seems to reduce the intermediate pool located between the two photosystems. If dark adapted cells are illuminated, mechanisms are established within about 20 s which appear to drain electrons from the intermediate pool.
NEAR ULTRAVIOLET INACTIVATION STUDIES ONESCHERICHIA COLI TRYPTOPHANASE AND TRYPTOPHAN SYNTHETASE
Authors: Coetzee Willem F. , Pollard Ernest C.
Published: January 2008

Abstract— –The response of two pyridoxal‐phosphate‐requiring enzymes of E. coli, tryptophanase and tryptophan synthetase, to near UV light (320–400 nm) has been studied. Tryptophanase is inactivated both in vivo and in vitro, but tryptophan synthetase is resistant to near UV under both conditions. This shows that near UV inactivation is not general for pyridoxal‐phosphate‐requiring enzymes. Substrate protection against light inactivation is demonstrated for tryptophanase. It is furthermore shown that pyridoxal phosphate is required for inactivation of this enzyme. However, the action spectrum for this inactivation does not coincide with the absorption spectrum of tryptophanase or of pyridoxal phosphate.
FLAVIN AS AN ACTIVE COMPONENT OF THE PHOTOREVERSIBLE PIGMENT SYSTEM OF THE GREEN ALGA PROTOSIPHON BOTRYOIDES KLEBS*
Authors: Thomas Jerry P. , O'Kelley Joseph C. , Hardman John K. , Aldridge Edward F.
Published: January 2008

Abstract— The photoreversible pigment system from Protosiphon botryoides Klebs can be separated into two fractions, which are individually inactive photobiologically, but can be recombined to form an active system. One fraction contains a component stable to combined heat and dilute acid treatment; this component can be replaced by flavin nucleotides. An essential component in the second fraction is heat labile. A similar pigment system has been isolated from other species of green algae.
AN UNUSUAL CASE OF PHOTOREACTIVATION OBSERVED IN AN INSECT EGG (SMITTIA SPEC, CHIRONOMIDAE, DIPTERA)*
Authors: Kalthoff Klaus
Published: January 2008

Abstract— An action spectrum for inactivation by ultraviolet (UV) radiation of Smittia eggs during intravitelline cleavage was established, taking into account wavelength‐dependent shielding of the effective targets. Under the assumption of a random distribution of the effective targets in the egg, the action spectrum displayed only one very distinct peak at 295 nm. The eggs were photoreactivable with an action spectrum similar but not identical to that found for direct photoreactivation (PR) in E. coli Indirect PR seems not involved because light was effective only after but not before UV. Temperature dependence and dose rate saturation could not be observed. The photoreactivable sector (PRS) was 0.75 after UV inactivation at 295 nm but only 0.32 after UV inactivation at 265 nm. Initial PR rates were highest after 295 nm and lowest after 265 nm. During migration of cleavage nuclei into the periplasm, when the shielding of nuclei by yolk material decreases by an order of magnitude, no corresponding increase in the sensitivity of the eggs to UV was observed. After inactivation at the blastoderm stage, when the nuclei are no longer shielded by yolk material, the PRS was also high (0.79) after UV of 295 nm but again lower (0.59) after 265 nm. These data are difficult to understand within the conceptual framework of light‐dependent enzymatic splitting of UV‐induced pyrimidine dimers in nucleic acids. Yet this type of PR seems to play a vital role in the survival of Smittia eggs under sunlight without need for pigmentation or shading.
PHOTOCHEMICAL QUANTUM EFFICIENCY AND ABSORPTION SPECTRA OF REACTION CENTERS FROM RHODOPSEUDOMONAS SPHAEROIDES AT LOW TEMPERATURE
Authors: Clayton Roderick K. , Yamamoto Tomoko
Published: January 2008

Abstract— The quantum efficiency of bacteriochlorophyll photo‐oxidation in reaction centers from Rhodopseudomonas sphaeroides is independent of temperature, within experimental accuracy of ± 15%, from 300 K to 5 K. Absorption spectra at low temperature show maxima at 532 and 544 nm corresponding to the two molecules of bacteriopheophytin in the reaction center. Comparison with the spectrum of the transient light‐induced state PF indicates that of these two molecules, only the one absorbing at 544 nm participates in forming PF.
PHOTOSENSITIZATION OF HUMAN DIPLOID CELL CULTURES BY INTRACELLULAR FLAVINS AND PROTECTION BY ANTIOXIDANTS
Authors: Pereira Olivia M. , Smith James R. , Packer Lester
Published: January 2008

Abstract— The damaging effects of near ultraviolet and visible light on WI‐38 human diploid lung fibroblasts were investigated. WI‐38 cells in culture were killed by light doses ranging from 2 to 10 × 103 W/m2 h. There was an inverse correlation between culture age, i.e. population doubling level and photosensitivity. However, this effect could not be related to capacity for DNA synthesis and cell division.

Flavins were clearly implicated as endogenous photosensitizers, and antioxidants such as d, l‐α‐tocopherol (vitamin E), BHT and ascorbic acid were found to afford the cells protection from light damage. Furthermore, products of lipid peroxidation could be detected in cell homogenates irradiated in the presence of ribofiavin.
PHOTOSENSITIVITY OF ARTIFICIAL BILAYER MEMBRANES: LIPID‐CHLOROPHYLL INTERACTION
Authors: Chen Chang‐Hwei , Berns Donald S.
Published: January 2008

Abstract— The interaction between lipid and chlorophyll in the photosensitive model bilayer membranes was studied by investigating the effects of the hydrocarbon chain length (6–20 carbons), degree of saturation (0–3 double bonds), and head group character of a series of synthetic and natural lipids on the membrane photoresponse. The results suggest, as a general phenomenon, that any stable membrane formed in the lipid‐chlorophyll a‐β‐carotene system is photosensitive regardless of the type of lipid in the membrane. The magnitude of the photoresponse (ΔV) varies for different lipids, and membranes containing natural phospholipids have a higher ΔV. The presence of chlorophyll a in a lipid solution enhances the lipid membrane stability.
DETAILED ACTION SPECTRUM FOR THE DELAY SHIFT IN PUPAE EMERGENCE OF DROSOPHILA PSEUDOOBSCURA*
Authors: Klemm Eva , Ninnemann Helga
Published: January 2008

Abstract— Dose‐response curves were measured for the delay phase shift of pupae emergence of Drosophila pseudoobscura. From these curves an action spectrum was determined for this process; it suggests a flavin to be the photoreceptor pigment.
PHOTOSYNTHESIS AS A RESOURCE FOR ENERGY AND MATERIALS*
Authors: Calvin Melvin
Published: January 2008

Abstract— Photosynthesis, both natural and as a model process, is examined as a possible annually renewable resource for both material and energy. The conversion of carbohydrate from cane, beets and other sources through fermentation alcohol to hydrocarbon may again become economic in the light of improved fermentation technology. It may also be possible to produce material by direct fermentation of relatively labile carbohydrates in seaweed. Even the direct photosynthetic production of hydrocarbon from known sources (Hevea, etc.), or newly bred ones, seems possible in view of the large number of species and the new techniques of plant cell cloning which have already been successful on sugar cane.

Finally, more distantly, synthetic systems constructed on the basis of our growing knowledge of the photosynthetic processes may produce fuel, fertilizer and power. Thus, from our current knowledge of the natural quantum conversion process in green plants we can envisage several photoelectron transfer processes. In a first one the excited sensitizer (chlorophyll) transfers its electron to an acceptor molecule such as an iron‐sulfur complex which, in turn, could either reduce a carbon compound or pass that electron into a hydrogen‐generating system leading to the evolution of molecular hydrogen. The remaining cation radical sensitizer would have to be neutralized through a chain of electron transfers which begins at another sensitized reaction (presumably by another kind of chlorophyll) through a quinone and other electron carriers. Finally, the last cation radical near the oxidation level of oxygen could be neutralized by electron transfer, ultimately from a water molecule (hydroxide or bicarbonate ion) involving a manganese catalyst.

Some steps in this sequence of transfers have already been demonstrated in synthetic systems. However, the actual physical construction of such a complete system is a much more complex task.
SOLVENT EFFECTS ON THE SPECTRA OF RETINAL SCHIFF BASES—11. MODELS FOR CONVERGENCE AND CLUSTERING OF VISUAL PIGMENT SPECTRA*
Authors: Milder S. J. , Kliger D. S.
Published: January 2008

Abstract— Electronic absorption spectra of retinal (A,) and 3‐dehydroretinal (A2) Schiff bases have been studied under a variety of solvent conditions. The spectra of the two species have different solvent dependencies. Variation in solvent conditions have a larger effect in the A2 spectra, although the wavelength maxima of A, and A, Schiff bases smoothly converge in solvents that shift them both to shorter wavelengths. Convergence curves for the A, and A2 Schiff bases can thus be generated in solution which resemble the convergence curves observed in visual pigments. It is also shown that the spectra of visual pigments made by combining A, and A2 with opsins from various fish species can be reproduced theoretically by changing the number of tryptophan or tyrosine side chains which are assumed to line the chromophore pocket. Discrete changes in the number of these side chains can exactly reproduce the clustering effect observed for a large variety of fish visual pigments. Variations in solvent characteristics which are analogous to possible chromophore environments in visual pigments have thus been shown to effect Schiff base spectra in such a way as to mimic the bathochromic shift, spectral convergence, and spectral clustering phenomena exhibited by visual pigments.
PHOTOSYNTHETIC OXYGEN EVOLUTION UNDER VARYING REDOX CONDITIONS: NEW EXPERIMENTAL AND THEORETICAL RESULTS
Authors: Greenbaum Elias
Published: January 2008

Abstract— The oxygen yield per flash of Chlorella in the presence of redox components such as benzo‐quinone, hydroquinone, Fe(CN)B‐ and IrC12‐‐ has been studied in an atmosphere of 10ppm 02. When oxidants are added to the cells, the familiar Joliot‐Kok oscillations with maximum yield on the third flash and periodicity four are observed. As hydroquinone is progressively added, the oscillations fade out and the steady state decreases. The pattern of O2 evolution approaches a monotonic climb to the steady state with no obvious oscillatory behavior. A novel method for analyzing this data has been developed. A simple fourth order linear difference equation with constant coefficients is presented. This equation is capable of describing the systematic transition from oscillatory to monotonic O2 yield.
RETARDATION OF ULTRAVIOLET LIGHT ACCELERATED CHLOROSIS BY VISIBLE LIGHT OR BY BENZYLADENINE IN NICOTIAN A GLUTINOSA LEAVES: CHANGES IN AMINO ACID CONTENT AND CHLOROPLAST ULTRASTRUCTURE*
Authors: Skokut Thomas A. , Wu J. H. , Daniel R. S.
Published: January 2008

Abstract— Low doses (180–720 Jm‐2) of ultraviolet light (254 nm) are known to accelerate the chlorosis of detached leaves in darkness. The development of such chlorosis is prevented by a photoreactivation treatment. However, we found that delayed light exposure or benzyladenine treatments (which were not effective in photorepair of UV‐induced thymine dimers in cell DNA) were also effective in retarding the UV‐accelerated chlorosis.

Small drops of benzyladenine solution placed on the UV irradiated leaf formed green islands which acted as strong sinks for the accumulation of free amino acids during dark incubation. To a lesser degree, non–irradiated green tissues surrounded by irradiated yellow leaf tissue also acted as sinks for amino acid accumulation.

The accelerated chlorophyll loss in UV‐irradiated leaves was correlated with degradation of chloroplast ultrastructure. Visible light or benzyladenine retarded this chloroplast degradation. The accelerated senescence of UV irradiated leaf tissue, therefore, is ultrastructurally and physiologically similar to normal senescence of detached dark‐incubated leaves, but progresses at a faster rate.

When the lower leaf surface was irradiated with high UV doses (3600–10,800 Jm‐2), the chloroplast ultrastructure of the spongy cells (except the envelope) was preserved for 3 days after dark incubation. However, the chloroplasts of the palisade cells were in a late stage of senescence. Since the spongy cells were dead (plasmalemma, tonoplast and chloroplast envelope disappeared), the maintenance of green color and ultrastructure of chloroplasts could have been due to inhibition of degrading enzymes normally associated with senescence.
CHEMISTRY OF SINGLET OXYGEN—XXV. PHOTOOXYGENATION OF METHIONINE*
Authors: Sysak P. Kevin , Foote Christopher S. , Ching Ta‐Yen
Published: January 2008

Abstract— Methionine (Met) photooxidation sensitized by rose bengal has been studied as a function of pH and other variables. At pH ≤ 6, the reaction is a simple one, 2 Met + O2→ 2 Methionine sulfoxide (MetO). At pH 6–10, another mechanism becomes important, leading to dehydromethionine; the structure of this compound was correctly assigned by Lavine (1945) as the heterocyclic N‐S compound 2. One mole of H2O2 is also produced in this process. Dehydromethionine hydrolyzes slowly to MetO. Above pH9, a process leading directly to MetO + H2O2 becomes important. The stoichiometry of the latter two processes are Met + O2+ H2O → MetO + H2O2; competition among these three processes accounts for the puzzling variations in O2 uptake. N‐Formylated derivatives of methionine undergo only the first and third processes. Substantial catalytic effects of buffers complicate the picture. All the reactions appear to involve singlet oxygen, since there is the predicted effect of D2O vs H2O on the rate of reaction, although the situation is complicated by apparent aggregation of Met above 5 mM.
CYTIDINE‐C(5)‐PHOTOEXCHANGE: A KINETIC ANALYSIS*
Authors: Hauswirth William , Wang Shih Yi
Published: January 2008

Abstract. –The kinetics of photolytic tritium exchange at C(5) of [5‐T]cytidine are analyzed in terms of the rate of cytidine light absorption in order to demonstrate its light‐induced nature as opposed to spontaneous exchange from a stable photoproduct. Corrections must be included for an inner filter effect and a spontaneous C(5)‐tritium exchange both due to cytidine photohydrate produced during UV exposure. The quantum efficiency of this C(5)‐photoexchange process is of the same order of magnitude as that for cytidine photohydration.
OSCILLATOR AND DIPOLE STRENGTHS FOR CHLOROPHYLL AND RELATED MOLECULES*
Authors: Shipman Lester L.
Published: January 2008

Abstract. –Previous calculations of the oscillator and dipole strengths for chlorophyll and related molecules are critically reviewed and, in some cases, important information that was not included in the original published reports is given. Oscillator and dipole strengths are reported for the Qy (0,0) vibronic transition of chlorophyll a, bacteriochlorophyll a, pyrochlorophyll a, pheophytin a, and pyrobacteriochlorophyll a. A medium correction has been explicitly included in the calculation of chlorophyll oscillator and dipole strengths. The proper formulas are summarized for the calculation of oscillator and dipole strengths from visible absorption spectra. Three criteria for the full specification of an oscillator strength or dipole strength calculation are recommended; (i) the formula used must be given explicitly, (ii) it must be made clear whether or not a medium correction was applied (and if a medium correction was applied, then it should be given explicitly), and (iii) the limits of integration over v must be specified.
THE PRIMARY REACTION OF PLANT PHOTOSYSTEM II
Authors: Knaff David B.
Published: January 2008

Abstract. …Research during the past five years has resulted in considerable advances in our understanding of the primary reaction (the initial light‐induced charge separation) of plant Photosystem II (the reaction responsible for the oxidation of H2O to O2). The primary reaction appears to involve the photooxidation of a specialized chlorophyll a and the concomitant photoreduction of a specialized plastoquinone. Evidence for this formulation of the Photosystem II reaction center and a discussion of the kinetic and oxidation‐reduction properties of the reactants are reviewed.
PHOTOTROPISM IN PHYCOMYCES MUTANTS LACKING β‐CAROTENE
Authors: Presti David , Hsu Wan‐Jean , Delbrück Max
Published: January 2008

Abstract. β‐carotene and riboflavin are considered as the major candidates for the photoreceptor for physiological responses to blue light in Phycomyces and a number of other organisms. Mutants of Phycomyces blocked in all six steps of the biosynthesis of β‐carotene from phytoene contain no detectable β‐carotene (less than 4 times 10‐5 of wild‐type amount) but exhibit phototropic responses identical to wild‐type. Moreover, wild‐type Phycomyces, while abundant in trans‐β‐carotene, contains no detectable cis‐β‐carotene, sometimes proposed as a photoreceptor candidate on the basis of the close similarity of the cis‐species absorption spectrum in the near UV region to many action spectra for blue‐light responses. These results indicate that β‐carotene cannot be the photoreceptor for phototropism in Phycomyces.
SOLVENT SENSITIVITY OF TYPE II PHOTOREACTIONS OF KETONES AS A DEVICE TO PROBE SOLUTE LOCATION IN MICELLES
Authors: Turro Nicholas J. , Liu Kou‐Chang , Chow Ming‐Fea
Published: January 2008

Abstract. The solvent sensitivity of the Type II reaction is employed as a device to investigate the properties of detergent solutions. The quantum yield for Type II reaction and the ratio of cleavage to cyclization are used as specific monitors of local solvent properties of micelles. Our results indicate that the average position of phenyl alkyl ketones is either on the micelle surface or in the Stern layer. The absence of significant residence time of the excited ketone in the aqueous phase is confirmed by the lack of quenching of Type II reaction by Eu3+ in micellar solutions.
THE FUNCTION OF PHYTOCHROME IN THE NATURAL ENVIRONMENT—IV. LIGHT QUALITY AND PLANT DEVELOPMENT
Authors: Holmes M. G. , Smith Harry
Published: January 2008

Abstract— Studies of the effect of light quality on the growth of Cucurbita pepo L. and Chenopodium album L. showed that large changes in morphological development can be induced by altering the proportion of red and far‐red in the incident radiation. Although phytochrome photoequilibria established at the beginning of the dark period affected development, similar changes were achieved with long term and continuous irradiation. The change in the growth pattern of C. album (a common weed species in cultivated land) caused by simulated wheat canopy shade, appeared to involve a redirection of growth towards processes which would achieve greater height at the expense of lateral growth. The evidence presented supports the hypothesis that phytochrome may be involved in the detection of mutual shading and the modification of development in an appropriate manner.
THE ROLE OF DIOXYGEN SPECIES IN THE BASE‐ AND COBALT‐CATALYZED OXYGENATION OF HINDERED PHENOLS
Authors: Nishinaga Akira , Itahara Toshio , Shimizu Tadashi , Tomita Haruo , Nishizawa Kanji , Matsuura Teruo
Published: January 2008

Abstract— The mechanisms by which 4‐substituted 2,6‐di‐t‐butylphenols are oxygenated by base‐ and Co(II) Schiff base complex‐catalysis into o‐ or p‐peroxyquinols and their Co(III) complexes, respectively, have been investigated. For the base‐catalyzed oxygenation, a one‐step ionic mechanism involving no radical species is suggested to be the most probable one. For the formation of the peroxycobalt(III) complexes, the following stoichiometry is concluded: ArOH + Co(II) + 5/4 O2→ peroxycobalt(III) complex + 1/2 H2O. A mechanism involving an electron transfer between the phenols and the Co(II)‐O2 complex followed by further electron transfer between the formed phenoxy radicals and the Co(II) complex to give the corresponding phenolate anions is proposed.
PULSE RADIOLYSIS STUDIES IN MODEL LIPID SYSTEMS: FORMATION AND BEHAVIOR OF PEROXY RADICALS IN FATTY ACIDS
Authors: Hasegawa K. , Patterson L. K.
Published: January 2008

Abstract— Radiolytic formation and peroxidation of fatty acid radicals have been investigated by pulse radiolysis techniques in oleate, linoleate, linolenate and arachidonate systems. A strong absorption band at 280 nm associated with conjugated radicals, Rconj, formed in polyunsaturated fatty acid moieties has been used as a probe for kinetic processes occurring at doubly allylic sites in the hydrocarbon chain. Formation of Rconj by O‐ has been found to be more efficient than the less selective OH radical. Peroxidation of Rconj is shown to be somewhat slower, (kR+ O2˜ 3 × 108M‐1 s‐1), than O2 reactions with radicals in oleate (kR+ O2= 1 × 109M‐1 s‐1). Peroxy radicals generated in these reactions disappear slowly by essentially second order processes (2kRO1˜ 107M‐1 s‐1). The superoxide radical, O‐2, shows little if any reactivity towards 0.01 M linolenate or arachidonate over periods of 20 s.
BINDING OF GLYCOLATE OXIDASE TO PEROXISOMAL MEMBRANE AS AFFECTED BY LIGHT
Authors: Roth‐Bejerano N. , Lips S. H.
Published: January 2008

The stability of the bond of glycolate oxidase to the peroxisomal membrane obtained from etiolated barley leaves, (Hordeum vulgareL. var Dvir) is affected by the pH of the homogenization medium. Peroxisomes isolated at pH 4 or 10 retain glycolic oxidase, while peroxisomes isolated at pH 69 loose this enzyme during centrifugation. Preillumination of whole seedlings, detached leaves or even homogenates changes the effect of pH on the retention of glycolate oxidase‐attachment which is strengthened at pH 9–10 and becomes very loose at pH 4–7. White and red light are responsible for the effect described. Far red light reverses this effect of red light.

Illumination induces a change in the isoelectric point (IpH) of peroxisomes without affecting the IpH of soluble enzymes. This red light‐induced change on IpH of microbodies is not reversed by far red light. The possible effects of light on peroxisomal membrane properties and on modulation of glycolate oxidase binding are discussed.
PHYTOCHROME ACTION: A REAPPRAISAL
Authors: Jose A. M. , Vince‐Prue D.
Published: January 2008

Stems of fully green plants show at least two types of response to light. In one, Pfr inhibits elongation. The second is a promotion of elongation which operates only in light; the effectiveness of red and far‐red wavelengths indicates that this response is also mediated through phytochrome. Studies of the de‐etiolation process also provide evidence for two modes of action of phytochrome; one is a Pfr‐dependent reaction, and the second requires continuous light (or frequent short irradiations).

It is proposed that, in addition to reactions which require Pfr and proceed in darkness, an important reaction of phytochrome in green plants occurs only in light. We have termed these two modes of action of phytochrome “static” and “dynamic”. The static mode operates after a brief exposure to light which establishes Pfr; the potential responses are largely reversible by far‐red and exhibit reciprocity. The dynamic mode operates only in light and the responses do not show reciprocity. We consider that this mode operates through the transition from one bound form of phytochrome to another. The possible involvement of these two modes of action of phytochrome in photoperiodic mechanisms is discussed.
PYRIMIDINE DIMER SITES ASSOCIATED WITH THE DAUGHTER DNA STRANDS IN UV‐IRRADIATED HUMAN FIBROBLASTS
Authors: Lehmann Alan R. , Kirk‐Bell Susan
Published: January 2008

Abstract. Pyrimidine dimer sites associated with the newly‐synthesized DNA were detected during post‐replication repair of DNA in UV‐irradiated human fibroblasts. These pyrimidine dimer sites were inferred from a decrease in the molecular weight of pulse‐labelled DNA after treatment with an extract of Micrococcus luteus containing UV‐specific endonuclease activity. In DNA synthesized immediately after irradiation the frequency of these daughter strand dimer sites was 7–20% of that in the parental DNA. Such sites were found in fibroblasts from normal donors and from xeroderma pigmentosum patients (with defects in excision‐repair or post‐replication repair). They were excised from the DNA of normal cells. As the time between UV‐irradiation and pulse‐labelling was increased, the frequency of dimer sites associated with the labelled DNA decreased. If the pulse‐label was delivered 6 h after irradiation of normal cells or excision‐defective xeroderma pigmentosum cells, no dimer sites were detected in the labelled DNA. It has usually been assumed that daughter‐strand dimer sites were the result of recombinational exchanges. The assay procedure used in these experiments and in similar experiments of others did not distinguish between labelled DNA containing pyrimidine dimers within the labelled section, and labelled DNA which did not contain pyrimidine dimers but was attached to unlabelled DNA which did contain dimers. The latter structures would arise during normal replication immediately following UV‐irradiation of mammalian cells. Calculations are presented which suggest that a significant proportion and conceivably all of the dimer sites associated with the daughter strands may have arisen in this way, rather than from recombinational exchanges as has been generally assumed.
ENERGY TRANSFER STUDIES ON CRYPTOMONAD BILIPROTEINS
Authors: MacColl Robert , Berns Donald S.
Published: January 2008

Abstract. Fluorescence techniques of various types have been used to study the light‐gathering and energy transfer modes for various cryptomonad biliproteins (phycocyanin or phycoerythrins). Analysis of fluorescence polarization and absorption data demonstrates that each cryptomonad biliprotein is composed of at least two distinct types of absorbing chromophore, each attached to the protein through covalent linkages to different polypeptide chains. Examination of the fluorescence emission spectra as a function of excitation at several wavelengths demonstrates that only one of these absorbing chromo‐phores is responsible for the fluorescence. This behavior is consistent with a known phenomenon whereby photons are gathered by more than one chromophore and then after radiationless energy transfer are emitted by only one chromophore.

Application of Förster dipole‐dipole energy transfer theory is made to the study of the mode by which energy absorbed by biliproteins migrates to Chl a. The spectral overlap integral between phycocyanin (Chroomonas sp.) and Chl a is 7.13 ± 10‐10cm6mol‐1and between phycocyanin and Chl c2 0.25 ± 10‐10cm6mol‐1. This large difference in overlap suggests, although does not prove, that phycocyanin might transfer energy directly to Chl a without a Chl c2 intermediary. The cryptomonad phycoerythrins may also use this method but a Chl c2 intermediate could not be ruled out for them. Radiationless energy transfer among homogeneous biliproteins is shown to be feasible. All these calculations are based on in vitro spectra and the interpretations extrapolated to the cellular situation, and these tentative conclusions are reached without knowledge of other factors, such as chromophore‐chro‐mophore orientation and distance, which could greatly influence the energy transfer scheme.
QUENCHING OF CHLOROPHYLL FLUORESCENCE BY NITROBENZENE
Authors: Beddard G. S. , Carlin Sheena , Harris L. , Porter G. , Tredwell C. J.
Published: January 2008

Abstract—Nitrobenzene quenching of chlorophyll fluorescence in ethanol has been investigated. Steady state relative quantum yields have been measured and fluorescence decay rates were determined using both nanosecond photon counting and picosecond pulses from a mode‐locked Nd3+ glass laser.

The fluorescence decay is described by

1(t)=I0 exp (‐t/τ−At1/2)

the form predicted for decay governed by the kinetics of the continuum model of diffusion controlled reactions. From the parameters of the fluorescence decay, the encounter distance is 5–7 A° the mutual diffusion coefficient is 0.62 × 10‐‐5 cm2s‐1± 12%.

Some of the fluorescence quenching is also attributed to static quenching by a nitrobenzene‐chlorophyll, ground‐state complex. The equilibrium constant for formation of this ground‐state complex was determined to be 4.1 M‐1. The combined dynamic and static quenching model allows calculation of quantum yields of fluorescence in good agreement with the experimentally determined quantum yields.
SPECTROSCOPY AND PHOTOCHEMISTRY OF BILIRUBIN PHOTOPRODUCTS. I. METHYLVINYLMALEIMIDE*
Authors: Kurtin William E.
Published: January 2008

Abstract— Methylvinylmaleimide, a product of the photooxidation of bilirubin, exhibits a broad luminescence band at approximately 450 nm on filter paper at room temperature. In methanol solvent, at 77 K, a broad phosphorescence band centered at 465 nm is observed. The experimental and theoretical spectroscopic properties of this compound are compared to those of the related molecules maleimide and phthalimide. Methylvinylmaleimide is photodegraded at pH 7.6 in a self‐sensitized reaction that in part involves singlet oxygen.
FLASH PHOTOLYSIS OF N‐ACETYL‐L‐TRYPTOPHANAMIDE: THE RELATIONSHIP BETWEEN RADICAL YIELDS AND FLUORESCENCE QUENCHING
Authors: Evans R. F. , Kuntz R. R. , Volkert W. A. , Ghiron C. A.
Published: January 2008

Abstract— The flash photolysis of N‐acetyl‐L‐tryptophanamide (NATA) in the presence of the fluorescence quenchers, imidazole, acrylamide and trichloroethanol, has been investigated. Imadazole and acrylamide induce a decrease in the NATA radical yield which correlates with their NATA fluorescence quenching action. These observations suggest that the fluorescent state is primarily responsible for the monophotonic photoionization processes. The acrylamide data also suggest that 40–65% of the NATA radicals arise from a long‐lived state (τ˜μs) which must originate from the fluorescent state. Unlike imidazole and acrylamide, trichloroethanol enhances the radical yield by reaction with excited state precursors. Mechanisms for the quenching of fluorescence and the long‐lived states are discussed.
CONVENIENT AND SIMPLE METHODS FOR THE OBSERVATION OF PHOSPHORESCENCE IN FLUID SOLUTIONS. INTERNAL AND EXTERNAL HEAVY ATOM AND MICELLAR EFFECTS
Authors: Turro Nicholas J. , Lru Kou‐Chang , Chow Ming‐Fea , Lee Plato
Published: January 2008

Abstract— Phosphorescence of organic molecules in fluid solutions may be conveniently and readily observed under certain conditions. If kp (radiative phosphorescence rate constant) is 10s‐1, then (in the absence of photoreaction) phosphorescence is observable upon N2 purging. For example, nitrogen purged, acetonitrile solutions of bromo and dibromonaphthalene display readily observable phosphorescence as a result of internal heavy atom enhancement of πS, and kp. External heavy atom enhancement of k, (CH2BrCH2Br solvent) of aromatic hydrocarbons even allows observation of phosphorescence from these compounds in N2 purged fluid solutions. Although bromonaphthalenes are not significantly phosphorescent in N2 purged aqueous solution, phosphorescence is readily observed in N2 purged detergent (HDTBr, HDTCl, and SDS) solutions above the critical micelle concentration. The general factors which determine whether phosphorescence is “readily” obervable in fluid solution are briefly discussed and the results are interpreted in light of these factors.
KINETICS OF FLUORESCENCE FADING OF ACRIDINE ORANGE‐HEPARIN COMPLEXES IN SOLUTION
Authors: Menter J. M. , Golden J. F. , West S. S.
Published: January 2008

Abstract— The irreversible photochemical fading of fluorescence of acridine orange‐heparin complexes indicates that fading involves the reaction of a “reactive” excited bound dye dimer with one in the ground state. A kinetic parameter, r“, is derived, which has a constant value over a considerable range of conditions, and which is directly related to rate constants for photophysical and photochemical processes. This parameter appears to be characteristic for heparin and may serve to identify it in the presence of other glycosaminoglycans.
QUENCHING OF TRIPLET STATES OF AROMATIC KETONES BY INDOLE AND 3‐METHYL INDOLE IN BENZENE SOLUTION. EVIDENCE FOR HYDROGEN‐ATOM ABSTRACTION, FOR QUENCHING DUE TO FAVOURABLE CHARGE TRANSFER INTERACTION AND FOR THE LACK OF ELECTRONIC ENERGY TRANSFER
Authors: Wilkinson Francis , Garner Anthony
Published: January 2008

Abstract— Quenching of the triplet states of the aromatic ketones (KCO), benzophenone, acetophenone and xanthone, by indole and 3‐methyl indole gives rise to the neutral radicals resulting from hydrogenatom transfer with variable efficiency (40–100%). Thus in addition to the reaction,

3KCO*+RH →KCOH +R.

some other quenching path or paths occur. There is no evidence for any triplet energy transfer even when this is energetically favourable, and it is suggested therefore that quenching to give ground state species following favourable charge‐transfer interactions accounts for the proportion of quenching without reaction.

The spectra of the indole radicals, R., were determined and the kinetics of their decay in aerated and deaerated solution were investigated and reaction schemes proposed to explain these observations.
CHEMISTRY OF SINGLET OXYGEN—XXVI. PHOTOOXYGENATION OF PHENOLSy†
Authors: Thomas Michael J. , Foote Christopher S.
Published: January 2008

Abstract— The aerobic dye‐sensitized photooxygenation of monohydric phenols proceeds by way of singlet oxygen under the conditions studied. Various phenols give different proportions of reaction with and quenching of singlet oxygen. Para‐substituted 2,6‐di‐t‐butylphenols show a linear correlation between the log of the total rate of singlet oxygen removal and their halfwave oxidation potentials; the same correlation is given for certain phenol methyl ethers. A Hammett plot using s̀+ gives ρ ‐ 1.72 ± 0.12, consistent with development of some charge in the quenching step. Reaction of photo‐chemically generated singlet oxygen with 2,4,6‐triphenylphenol gives 2,4,6‐triphenylphenoxy radical as an intermediate in singlet oxygen quenching, although no overall reaction occurs. Kinetic analysis indicates that the radical is derived exclusively from the interaction of 2,4,6‐triphenylphenol with singlet oxygen. A charge‐transfer mechanism for quenching of singlet oxygen by phenols is proposed.
PHOTODYNAMIC INACTIVATION OF E. COLI BY ROSE BENGAL IMMOBILIZED ON POLYSTYRENE BEADS
Authors: Bezman S. A. , Burtis P. A. , Izod T. P. J. , Thayer M. A.
Published: January 2008

Abstract. The photodynamic inactivation of E. coli by visible light and O2 was found to occur in the presence of the sensitizer rose bengal, immobilized by covalent bonding to polystyrene beads. The demonstrated absence of significant amounts of dissolved rose bengal indicated that an inactivation mechanism based on penetration of sensitizer molecules into the cell's interior could not be operating. Survival curves typically exhibited induction periods followed by rapid exponential death, with 99.99% kill requiring 1–2 h depending on conditions. A mechanism involving the participation of photo‐generated singlet excited oxygen O2(1δ) in inactivation of E. coli is proposed. The photodynamic inactivation rate increased significantly in H2O compared with H2O, which is evidence supporting singlet oxygen as an active intermediate, since O2(1δ) has a much longer lifetime in H2O than in H2O. H2O did not act as a short term poison in the absence of sensitizer.
PHOTOEFFECTS OF PIGMENTED LIPID MEMBRANES IN A MICROPOROUS FILTER
Authors: Mountz James M. , Tien H. Ti
Published: January 2008

Abstract. The light‐induced voltage and current generated by pigmented lipid membranes have been investigated. The membranes, separating two aqueous solutions, were formed in microporous filters with pore sizes ranging from 0.05 to 8μm in diameter and densities of 105 to 6 × 108 pores/cm2. The structure and some physicochemical properties of these membranes are described and compared with those of planar BLMs. Photopotentials up to 400 mV could be developed across these membranes having an effective current of 21μA‐cm‐2. These and other parameters (redox couples and lifetime) were studied over a period of days. The advantages of this membrane system such as long‐term stability and manipulability are discussed.
SOLVENT AND METHYL SUBSTITUENT EFFECT ON PHOTOTAUTOMERISM AND IONIZATION OF ALLOXAZINES
Authors: Koziolowa Anna
Published: January 2008

Abstract—The absorption and emission spectra of alloxazine and its methyl derivatives have been measured in solvents of different polarity. From roughly linear correlation between two long wavelength absorption maxima and the emission maxima positions vs solvent polarities. systematic deviations have been observed for alloxazines in pyridine, acetic acid and water. The deviations depend on the methylation site of alloxazine in a way suggesting formation of hydrogen bond in the ground state and phototautomerism in the excited state. As phototautomerism of alloxazines in the presence of pyridine and water may involve ionic equilibria, the pKavalues of alloxazines have been measured (8.11–8.58) and the pKB*estimated from the Förster cycle (2.3–6.6 for N‐1 monoanion and 7.4–7.8 for N‐3 monoanion). The phototautomeric efficiency of alloxazines in pyridine, acetic acid and water depend on the acidity of the N‐1 proton and on the steric effects of methyl substituents, mainly at C‐9. The anionic forms of alloxazines differ from the phototautomeric species in emission maxima positions, radiative lifetimes and they are dissimilarly influenced by the methylation site and medium viscosity.
WAVELENGTH DEPENDENCE AND KINETICS OF UV‐INDUCED FREE RADICAL FORMATION IN THE HUMAN CORNEA AND LENS
Authors: Yamanashi B. S. , Hacker H. , Klintworth G. K.
Published: January 2008

Abstract— The wavelength dependence of free radical formation in the human lens and cornea was obtained in the ultraviolet‐visible (UV‐VIS) range with electron paramagnetic resonance. The spectral feature of having their maxima close to 290 nm, negligible intensity above 320 nm, and appreciable intensity toward 260 nm is common to both of these tissues.

The kinetics of free radical formation in the lens and cornea was interpreted in terms of a two component exponential function with characteristic rate constants kl and k2, the latter of which has the same value for both the lens and cornea.
COMPLEX FORMATION BETWEEN ALCOHOLS AND THE AROMATIC HYDROCARBONS PYRENE AND 1‐METHYLPYRENE
Authors: Lianos P. , Georghiou S.
Published: January 2008

Abstract—Pyrene and 1‐methylpyrene have been shown by infrared spectrometry to form 1:I molecular complexes with alcohols at a concentration of 0.02 M in CCl4 solutions. The association constants are of the order of 1 M‐1. The fluorescence decay profiles of 10μM pyrcnc in dilutc butanol‐heptane solutions have been found to be the sum of two exponential components in agreement with ground state complex formation
ON THE ROLE OF FORBIDDEN LOW‐LYING EXCITED STATES OF LIGHT‐HARVESTING CAROTENOIDS IN ENERGY TRANSFER IN PHOTOSYNTHESIS*
Authors: Thrash R. J. , Fang H. L‐B. , Leroi G. E.
Published: January 2008

Abstract—It is proposed that the low‐lying. electric‐dipole forbidden Ag excited electronic state recently discovered in β‐carotene acts as the energy donor in Förster‐type excitation transfer to antenna Chl molecules folbwing β‐carotene's light‐harvesting function in photosynthesis. The mechanism and conclusion should apply as well to all carotenoid accessory pigments.
ON THE PRODUCTION OF NITROXIDE RADICALS BY SINGLET OXYGEN REACTION: AN EPR STUDY
Authors: Lion Y. , Gandin E. , Van de Vorst A.
Published: January 2008

Abstract— The production of free radicals by reaction of 2,2,6,6‐tetramethyl‐4‐piperidinol with singlet oxygen was studied by EPR spectroscopy. The rate constant of the amine was found to be equal to 8 ×105M‐1s‐1 in ethanol and to 4 × 107M‐1s‐1 in phosphate buffer (pH 8). Competition experiments were performed with singlet oxygen quenchers such as NaN3, DABCO and the quenching rate constants were found to be consistent with the literature values. The EPR method proved to be a valuable technique to study the reaction of singlet O2 with the sterically hindered amine without any interfering effect.
KINETIC ANALYSIS OF THE INFLUENCE OF HYDROSTATIC PRESSURE ON BIOLUMINESCENCE OF GONYAULAX POLYEDRA
Authors: Gooch Van , Vidaver William
Published: January 2008

Abstract— Hydrostatic pressure was used as a probe to examine control mechanisms of bioluminescence in Gonyaulax polyedra. The initial effect of a pressure increase step is both to increase the intensity of the continuous light emission (glow) of the entire cell population and to increase the frequency of discrete flashes arising from single cells. Following the pressure application, however, the glow does not merely attain a new level but rather goes through various transient changes, whereby the kinetics of these changes are faster with a given higher pressure. A qualitative fit to several aspects of the pressure induced glow kinetics was generated by a simple reaction rate theory model. The effect of pressure upon the circadian rhythm control of bioluminescence was also investigated with the result being that no significant influence was observed under the experimental conditions.
IMPROVED ANALYTIC CHARACTERIZATION OF ULTRAVIOLET SKYLIGHT
Authors: Green A. E. S. , Cross K. R. , Smith L. A.
Published: January 2008

Abstract— We present an improved analytic characterization of diffuse spectral irradiance (skylight) for the wavelength range 280–380 nm and solar zenith angle range from 0 to 85°. The formulas achieve greater accuracy by (a) focusing on ratio representations and (b) adjusting the parameters to the more precise radiative transfer calculations of Dave, Braslau and Halpern.
QUENCHING OF A RETINAL TRIPLET STATE BY A NITROXYL RADICAL
Authors: Kuzmin V. A. , Kliger D. S. , Hammond G. S.
Published: January 2008

Abstract— The long lived triplets from all‐trans retinal and 11‐cis retinal are quenched by a nitroxyl radical, 4‐hydroxy‐2,2,6,6‐tetramethylpiperidinoyl, with essentially identical rate constants. The rates vary with solvent but do not correlate with solvent polarity. The results confirm implications of earlier work with oxygen quenching and are compatible with the view that isomerization occurs in non‐relaxed triplets or that the triplet (or triplets) observed spectroscopically decay by way of a single triplet state which has a small electronic energy gap to ground state isomers.
CIRCADIAN RHYTHM OF EXTRARETINAL PHOTOSENSITIVITY IN HATCHLING ALLIGATORS, ALLIGATOR MISSISSIPPIENSIS
Authors: Kavaliers Martin
Published: January 2008

Abstract—

Hatchling American alligators, Alligator mississippiensis, display a diel rhythm of extra‐retinal (non‐pineal) photosensitivity. There is a bimodal pattern in the threshold fluence rate required for initiating and effecting extra‐retinally‐mediated phototaclic responses. Significantly greater threshold fluence rates are required in the photophase than the scotophasc of a 12 h light: 12 h dark cycle. Under constant darkness there continues an endogenous, apparently circadian rhythm of extra‐retinal photosensitivity. In all cases there is a significantly greater photosensitivity at lower temperatures.
GERMICIDAL ULTRAVIOLET LIGHT INDUCES ORNITHINE DECARBOXYLASE IN MOUSE EPIDERMAL CELLS AND MODIFIES THE INDUCTION CAUSED BY PHORBOL ESTER TUMOR PROMOTERS
Authors: Lichti Ulrike , Bowden G. Timothy , Patterson Elroy , Ben Theresa , Yuspa Stuart H.
Published: January 2008

Abstract—

Germicidal ultraviolet light (UVC. 8–10 J/m2) induces ornithine decarboxylase (ODC) in mouse epidermal cells in vitro in a biphasic manner with maxima of 2–3 fold induction at 4–6 h and of 10–20 fold induction at 15–18 h after irradiation. At this dose of UVC overall protein synthesis is inhibited by 10–30% and RNA synthesis by 40–50%. Induction of both ODC peaks is prevented by actinomycin D or cycloheximide. Similar culture factors appear to influence the extent of ODC induction by UVC and by the tumor promoter, 12‐O‐tetradecanoyl phorbol‐13‐acetate (TPA), since the ratio of peak activities is approximately constant at 2, whereas absolute values vary considerably between experiments. If cells are irradiated with UVC and then exposed to TPA, the effects are additive at 10 J/m2, less than additive at higher and enhanced at lower doses of UVC.