bluuebunny/crossref_metadata_2025 huggingface dataset:
ETUDE PAR FLUORESCENCE DE BASES DE SCHIFF DU PYRIDOXAL, COMPARAISON AVEC LA L ASPARTATE‐AMINOTRANSFERASE
Authors: ARRIO‐DUPONT M.
Published: January 2008

Abstract— –Absorption and emission spectra of Schiff bases of pyridoxal‐HCI or pyridoxal‐5‐phosphate with L‐valine, n‐butylamine or N‐α‐acetyl‐L‐lysine‐N‐methylamide have been studied as a function of pH. We can write the complete ionization diagram and equilibria. The results of Martell[6] are confirmed: the forms analogous to the coenzyme in aspartate aminotransferase, which absorb at 410 nm and 360 nm (or 340 nm for the Schiff base with n‐butyl‐amine) have the phenol OH ionized; the imine nitrogen is protonated for species absorbing at 410nm (in the enzyme: inactive form and complex with aminoacid) and unprotonated for species absorbing at 360 nm (in the enzyme, active form). Their fluorescence wavelengths are respectively 500 nm and 430 nm. Protonation of the pyridine nitrogen of these forms does not shift the absorption band; the fluorescence intensity is 20‐fold greater for the N‐protonated forms.

The real pK of the imine nitrogen is 8.5 ±0.8 for species with pyridine N‐protonated or 10.4 for the non‐protonated forms. The observed pK 6.3 in the enzyme can be explained if the imine nitrogen is hydrogen bonded to an amino‐acid side chain of the protein: lysine, tyrosine, serine, sulfhydryl.

The quantum yield of the coenzyme fluorescence in the enzyme has been compared to that of the analogous Schiff base (absorbing at the same wavelength). According to the results, we cannot deduce whether the pyridine nitrogen is protonated in pyridoxal form of the enzyme.

If it is protonated, as in the pyridoxamine form, the coenzyme environment is not the same in the two forms. If the pyridine nitrogen is unprotonated in the pyridoxal form and protonated in the pyridoxamine form, the environment of the coenzyme is the same in these two forms of the enzyme.
MUTAGENIC EFFECTS OF NEAR ULTRAVIOLET AND VISIBLE RADIANT ENERGY ON CONTINUOUS CULTURES OF ESCHERICHIA COLI*
Authors: WEBB ROBERT B. , MALINA MYLAN M.
Published: January 2008

Abstract— –The induction of mutation to phage T5 resistance by near ultraviolet (u.v.) and visible light was studied in chemostat cultures of Escherichia coli strains B/r and B/r/1, trp. The visible light mutation rate to phage T5 resistance was independent of growth rate over the range studied. This result is consistent with a photochemical mechanism of mutagenesis. Changeovers, in which a faster growing subpopulation takes over the culture, usually causing the mutant frequency to decline sharply, occur more frequently in chemostat cultures irradiated with visible light than in cultures treated with far u.v. or caffeine. A preliminary action spectrum was obtained with aerated chemostats that revealed effective wavelengths to be between 330 nm and 500 nm. Wavelengths longer than 500 nm were not effective. Wavelengths longer than 340 nm were not mutagenic in anaerobic chemostats. This oxygen requirement for mutagenesis between 340 nm and 500 nm is consistent with a photodynamic mechanism of action. In aerated cultures, wavelengths between 400 nm and 500 nm were as effective as wavelengths between 330 nm and 400 nm. A number of naturally occurring compounds, including riboflavin and vitamin K, are consistent with the data as candidates for the chromophore responsible for near u.v. and visible light mutagenesis.
FLUORESCENCE OF THYMINE IN AQUEOUS SOLUTION AT 300° K
Authors: HAUSWIRTH WILLIAM , DANIELS MALCOLM
Published: January 2008

Abstract— –Fluorescence of thymine in neutral aqueous solution at room temperature has been detected using the multiscaling operation of a multichannel analyzer. The emission maximum (2.96 μm‐1) and 0‐0 transition energy (3.37‐3.45 μm‐1) are close to those determined at liquid nitrogen temperature in mixed solvents. The quantum efficiency of fluorescence excited at 3.77 μm‐1 is calculated to be 1.04 × 10‐4.

The corrected relative excitation spectrum shows significant differences from the absorption spectrum when both are determined under identical conditions of concentration and spectral bandwidth on the same instrument. The quantum yield of fluorescence decreases about 2‐fold as the energy of excitation is increased beyond the 0‐0' transition and follows the relation 1/φ°αEexcit..

This behavior is discussed in terms of (a) nπ* and ππ* states, (b) emission from a minor tautomer and (c) kinetics of competing deactivation processes.
LUMINESCENCE IN PHOTOSYNTHETIC BACTERIA*
Authors: FLElSCHMAN DARRELL E.
Published: January 2008

Abstract— The behavior of glow curves and of ferricyanide‐induced luminescence in photo‐synthetic bacteria is consistent with a model in which light is emitted when electrons return to oxidized reaction center chlorophyll from the primary acceptor. A number of observations can be explained if it is assumed that the chromatophore membrane potential provides part of the activation energy for the process. The model is tested by inducing light emission by the generation of potassium diffusion potentials in preilluminated Chromatium chromatophores.
STUDIES ON SOME INTERMEDIATES AND PRODUCTS OF THE PHOTOREDUCTION OF 9,10‐ANTHRAQUINONE *,†
Authors: CARLSON STEVEN A. , HERCULES DAVID M.
Published: January 2008

Abstract— The mechanism of the photoreduction of 9,10‐anthraquinone (AQ) in alcohol and hexane has been studied by flash photolysis. The fluorescence spectrum of the photoproduct, 9,10‐dihydroxy anthracene shows a large shift between hexane and ethanol. The quantum yields of photoreduction for AQ are solvent‐dependent, the reaction between the solvent radical and AQ determining the quantum yield.

The absorption spectrum of the 9,10‐anthrasemiquinone (AQH.) has a long‐wavelength absorption band with peaks at 631 and 678 nm. The second‐order decay constants for AQH. were estimated to be 1.3 × 109, 6.7 × 108 and 2.0 × 108M‐1 sec‐1 in ethanol, 2‐propanol and ethylene glycol, respectively.

A long‐wavelength absorption band was observed for 9,10‐anthrasemiquinone radical anion, having peaks at 776 and 860 nm; epsi;max= 1900 at 776 nm. This spectrum is compared with the spectra of 9,10‐dihydroxy anthracene mono‐ and di‐anions. The 9,10‐anthrasemiquinone radical anion was found to photoreduce quantitatively to 9,10‐dihydroxy anthracene mono‐anion with a quantum yield of 0.1.
FLASH PHOTOLYSIS‐ELECTRON SPIN RESONANCE: A KINETIC STUDY OF ENDOGENOUS LIGHT‐INDUCED FREE RADICALS IN REACTION CENTER PREPARATIONS FROM RHODOPSEUDOMONAS SPHEROIDES*
Authors: Bolton James R. , Cost Konstantine
Published: January 2008

Abstract— Using the technique of flash photolysis‐electron spin resonance, we have detected, by means of a kinetic analysis, a rapidly decaying signal in reaction center preparations from the R26 blue‐green mutant of Rhodopseudomonas spheroides. This signal, which we designate Signal B3, is essentially the same as that seen previously in iron‐free preparations. Signal B3 decays at 20°C with a 1/e time of ˜ 3 ms and exhibits an activation energy of 5 ± 1 kcal mol‐1 over the temperature range 0–30°C. Extraction with isooctane completely eliminates Signal B3, whereas readdition of exogenous ubiquinone‐30 completely restores the signal. o‐Phenanthroline has no effect on Signal B3. We discuss these results in terms of a model in which the primary acceptor is an iron‐ubiquinone complex with excess ubiquinone serving as a secondary electron acceptor pool.
STUDIES ON THE PROTEIN CONFORMATION OF PHYTOCHROME
Authors: Tobin Elaine M. , Briggs Winslow R.
Published: January 2008

Abstract— The extinction coefficients for large rye phytochrome were found to be: Fluorescence and circular dichroism spectra of large‐ and small‐molecular‐weight rye phytochrome give no evidence for a protein conformational change on phototransformation of phytochrome. The large molecule has a fluorescence emission peak at 331 nm when excited at 290 nm, and an excitation peak for this emission at 288 nm. The circular dichroism spectra indicate that large rye phytochrome has about 17–20% a‐helix content, 30%β‐structure and 50% random coil, and that the small rye phytochrome has about 10–13%α‐helix content. The ultraviolet difference spectra for large and small rye phytochrome are similar and differ from the difference spectrum of the small oat phytochrome in the relative size of the 296–298 nm peak. The difference spectra may reflect changes in chromophore absorbance and in the environment of amino acid residues near the chromophore, particularly of tyrosine, and perhaps of tryptophan and cysteine.
CELLULAR REACTIVATION OF ULTRAVIOLET‐IRRADIATED HUMAN ADENOVIRUS 2 IN NORMAL AND XERODERMA PIGMENTOSUM FIBROBLASTS
Authors: DayIII Rufus S.
Published: January 2008

Abstract— A plaque assay for adenovirus 2 on normal human fibroblasts has been developed and used to measure the survival of ultraviolet‐irradiated virus on six human fibroblast cell lines. When four xeroderma pigmentosum cell lines were used as viral hosts, an average of one lethal event per virus in the viral population was made with 10, 15, 62, and 78 J m‐2 respectively, while using two normal cell lines as hosts, 197 and 205 J m‐2 were required to inflict the same damage. These differences are attributed to the known repair deficiency of xeroderma pigmentosum cells, and are discussed in the light of previous data obtained using other animal viruses.
THE DOSE RESPONSE CURVE IN PHYTOCHROME‐MEDIATED ANTHOCYANIN SYNTHESIS IN THE MUSTARD SEEDLING
Authors: Drumm H. , Mohr H.
Published: January 2008

Abstract—The dose response curve for light (phytochrome)‐induced anthocyanin synthesis was determined in the mustard seedling. The curve gives the amount of anthocyanin (A) synthesized within 24 h as a function of the amount of Pfr* produced by a brief light pulse. The [Pfr] response curve is composed of two linear parts with very different slopes (a1,2) connected by a relatively narrow transient range (curved segment). The [Pfr] response curve extrapolates precisely through zero [Pfr]. The reciprocity law is valid over the whole range investigated (up to 320 s of irradiation). It is concluded that the initial (or primary) reaction of Pfr (Pfr+ X → PfrX) does not involve any significant cooperativity in the case of phytochrome‐mediated anthocyanin synthesis. It is speculated that the linear parts of the [Pfr] response curve truly reflect the mode of phytochrome action (A=a1,2 [Pfr]; X does not come into play since it is not rate limiting) whereas the curved segment represents a transition of the reaction matrix of Pfr. The large difference between a1 and a2 seems to indicate that the physiological effectiveness of a given amount of Pfr (or PfrX) is determined by [Pfr] through a Pfr‐induced change in the reaction matrix.
PHOTOREDUCTION OF PROTOCHLOROPHYLL AND ITS DERIVATIVES
Authors: Suboch V. P. , Losev A. P. , Gurinovitch G. P.
Published: January 2008

Abstract—Photoreduction of protochlorophyll and a series of its derivatives (with gradual simplification of the structure) was studied in ascorbic acid‐propanol‐pyridine mixtures. Additions were introduced into the solutions to suppress some side processes. Conditions were found for the photoreduction of pigment on the 7,8‐linkage, with the formation of corresponding chlorins. Chlorin yields depended on the nature of the metal in the centre of the pigment molecule. The yield of chlorophyll upon photoreduction of protochlorophyll was 30 per cent, and the yields of Zn‐derivatives of protochphyll was about 35–80 per cent. Photochemically prepared chlorins were isolated by chromatography. Some differences were discovered between their electronic, infrared, and nuclear magnetic resonance spectra and those of natural chlorins. These differences result from chlorins with a cis arrangement of hydrogen atoms on the 7,8‐linkage being selectively formed upon photoreduction, while natural chlorins have the trans arrangement. The mechanism of the photoreduction reaction is discussed.
TRIPLET STATES OF UBIQUINONE ANALOGS STUDIED BY ULTRAVIOLET AND ELECTRON NANOSECOND IRRADIATION
Authors: Amouyal E. , Bensasson R. , Land E. J.
Published: January 2008

Abstract—The triplet excited states of four derivatives of ubiquinone‐30, in which various ring substituents are progressively altered, have been studied by laser flash photolysis (265 nm) and pulse radiolysis (9–12 MeV electrons). Triplet absorption spectrum, extinction coefficient, lifetime, energy level and quantum efficiency of formation were determined. By comparison with previous studies with ubiquinone‐30, it is deduced that the low triplet energy and quantum efficiency of formation of triplet ubiquinone‐30 is caused by the presence of the two adjacent methoxy substituents, rather than to the isoprenoid side chain. The low quantum efficiency of triplet formation, although consistent with in vivo ubiquinone photomodification occurring via the triplet, suggests that little of the ubisemiquinone observed in bacterial photosynthesis is formed via excited ubiquinone.
OCCURRENCE OF THE SINGLET‐OXYGEN MECHANISM IN PHOTODYNAMIC OXIDATIONS OF GUANOSINE*
Authors: Saito Isao , Inoue Kenzo , Matsuura Teruo
Published: January 2008

Abstract—Photosensitized oxidations of guanosine in aqueous methanol were investigated with a variety of sensitizers, and several experimental tests for the participation of singlet oxygen were examined. It has been shown that the dye‐sensitized photooxidation of guanosine proceeds by both singlet‐oxygen and Type I mechanisms, and that the efficiency of the singlet‐oxygen mechanism is strongly dependent on photosensitizer type.
PRIMARY MECHANISMS OF ERYTHROCYTE PHOTOLYSIS INDUCED BY BIOLOGICAL SENSITIZERS AND PHOTOTOXIC DRUGS
Authors: Nilsson Robert , Swanbeck Gunnar , Wennersten Goran
Published: January 2008

Abstract— The elucidation of the molecular mechanism of photosensitized hemolysis of red blood cells may give important clues to the primary events underlying the phototoxic reactions observed in pathological conditions such as porphyria and induced by photosensitizing drugs. Sensitizers effective in photo‐hemolysis are porphyrins, the tryptophan metabolite kynurenic acid, and phototoxic drugs such as chlor‐promazine and demethylchlortetracycline. Utilizing the singlet oxygen quenchers. jS‐carotene and histi‐dine and the large deuterium effect on the lifetime of singlet oxygen previously described by us, good evidence of the participation of this excited molecular species in the photohemolysis in the presence of kynurenic acid was obtained. Chlorpromazine and demethylchlortetracycline clearly act by a non‐singlet oxygen pathway. The situation observed with haematoporphyrin is less clear and may represent a mixed Type I‐Type II mechanism.
EFFECTS OF NEAR‐ULTRAVIOLET and VIOLET RADIATIONS (313–405 NM) ON DNA, RNA, and PROTEIN SYNTHESIS IN E. COLI B/r: IMPLICATIONS FOR GROWTH DELAY*
Authors: Ramabhadran T. V.
Published: January 2008

Abstract— Fluences (21–32 kJ/m2) of near‐ultraviolet radiation that induce about a 1‐h growth delay in continuously growing cultures of E. coli B/r are found to produce complete cessation of net RNA synthesis, while the effects on protein and DNA synthesis are considerably milder. The near‐UV action spectrum for this inhibition of RNA synthesis is similar to the action spectrum for growth delay in E. coli B and to the absorption spectrum of E. coli valyl transfer RNA. In addition, the fluences required for inhibition of RNA synthesis and for growth delay are similar to those reported for formation of 4‐thiouridine‐cytidine adducts in transfer RNA. These findings suggest that the chromophore and target for near‐UV‐induced inhibition of both net RNA synthesis and growth in E. coli may be 4‐thiouridine in transfer RNA.
INTRAMOLECULAR ENERGY TRANSFER IN NATIVE tRNA AT ROOM TEMPERATURE
Authors: Ballini Jean‐Pierre , Vigny Paul , Thomas Gilles , Favre Alain
Published: January 2008

Abstract— The odd nucleoside 4‐thiouridine, which is present in position 8 of 70% of E. coli tRNAs, possesses unusual spectroscopic properties which make it suitable for intramolecular energy transfer studies. Both its luminescence excitation spectrum and the action spectrum (230–380 nm) for the 8–13 link formation have been established in native E. coli tRNA at room temperature. The spectra are identical and present a new unexpected peak around 260 nm. At this wavelength, they are amplified by a factor of nine as compared with the absorption and excitation spectra of the free nucleoside in aqueous solution.

The origin of this new peak is discussed and it is concluded that energy transfer does occur from the common nucleosides to the 4‐thiouridine residue. Using the values of the nucleosides to 4‐thiouridine distances inferred from the sets of atomic coordinates obtained on yeast tRNAphe crystals, a satisfactory account of our finding can be obtained assuming singlet‐singlet energy transfer. The efficiency of the mechanism is probably favoured by a good overlap between the emission spectra of the common nucleosides and the absorption spectrum of 4‐thiouridine.
EMISSION SPECTRUM DIFFERENCES IN FLUORESCENT BLACKLIGHT LAMPS
Authors: Forbes P. D. , Davies R. E. , D'Aloisio L. C. , Cole C.
Published: January 2008

Two types of fluorescent blacklight lamps with distinctly different emission spectra bear the same code designations. One type, which we refer to as BL‐O, has most of its UV radiation emission centered over 350 nm. The other (BL‐N) type concentrates more energy around 365 nm. The spectral differences are correlated with the manufacturer's shift in the type of phosphor used in the lamps. Whether this change is detrimental to photobiological experiments depends in part on the user's ability to independently verify emission spectra.
THE SPECTRAL DISTRIBUTION OF THE LUMINESCENCE EMITTED DURING GROWTH OF THE YEAST SACCHAROMYCES CEREVISIAE AND ITS RELATIONSHIP TO MITOGENETIC RADIATION
Authors: Quickenden Terence I. , Hee Shane S. Que
Published: January 2008

Abstract— The spectral distributions of two previously reported weak luminescences from liquid cultures of the yeast Saccharomyces cerevisiae have been determined. During the logarithmic phase of growth, emission was observed as a broad UV band between 200 and 425 nm, and as a visible region band between 525 and 700 nm. During the stationary phase, there were two narrow bands centred at 250 and 650 nm, and a broad band extending from 325 to 525 nm. The UV components are compared with Gurwitsch's mitogenetic radiation, and possible chemical and radiolytic sources of the luminescences are discussed.
DIRECT PHOTO‐AFFINITY LABELING OF CYCLIC NUCLEOTIDE BINDING PROTEINS WITH GUANOSINE‐3‘,5’‐MONOPHOSPHATE
Authors: Antonoff R. S. , Ferguson J. J. , Idelkope G.
Published: January 2008

Abstract— Radioactivity from [3H]‐guanosine‐3′,5′‐monophosphate was shown to become stably linked to proteins in testis extracts during ultraviolet irradiation. Adenosine‐3′,5′‐monophosphate competitively inhibited incorporation into these proteins. Guanosine‐3′,5′‐monophosphate had a lower affinity for binding sites than did adenosine‐3′,5′‐monophosphate. Similar peptides were photo‐labeled with [3H]‐guanosine‐3′,5′‐monophosphate and [3H]‐adenosine‐3′,5′‐monophosphate. Guanosine‐3′,5′‐monophosphate was more efficiently incorporated than was adenosine‐3′,5′‐monophosphate. Extracts from a number of tissues incorporated both cyclic nucleotides photochemically.
THE SINGLET OXYGEN REACTIVITY OF BILIVERDIN
Authors: Mathewn I. B. C. , Toledo M. M.
Published: January 2008

Abstract— In 1, 1, 2‐trichlorotrifluoroethane solution biliverdin physically quenches singlet oxygen at a rate of 8 × l0sM‐1s‐1 and reacts chemically at 6 × 10 5M‐1s‐1 to give a red product. In D, O solution the rate constants are PD dependent and range from 1.5–6 times 1010M‐1s‐1 for quenching and the chemical rate varies from 3–5 × 108 M‐1 s‐1 to give colorless products.
THE PHOTOCHEMISTRY OF RIBOFLAVIN—V. THE PHOTODEGRADATION OF ISOALLOXAZINES IN ALCOHOLIC SOLVENTS
Authors: Moore William M. , Ireton Robert C.
Published: January 2008

Abstract— Riboflavin and other N‐10 substituted isoalloxazines have been irradiated anaerobically in alcohols and alcohol‐water mixtures. Deuterium substitution was used in several different ways to determine the hydrogen kinetic isotope effect. Riboflavin and 10‐(3′‐hydroxypropyl)‐isoalloxazine were photobleached in 2‐propanol, 2‐propanol‐0‐d, 2‐propanol‐2‐d, t‐butyl alcohol, and t‐butyl alcohol‐0‐d. No isotope effect significantly different from 1.0 was found for any of the nondeuterated to deuterated solvent comparisons. When the anaerobic irradiation of 10‐(3′‐hydroxypropyl‐3′,3′‐d2)‐isoalloxazine and 10‐(3′‐hydroxypropyl)‐isoalloxazine in either 2‐propanol or t‐butyl alcohol were compared, kinetic isotope effect ratios for H to D of 2.8 were obtained. Thin layer chromatography in conjunction with color return at 445 nm during oxidation showed that lumichrome and formylmethylflavin, which are irreversible photodegradation products, were formed from the photoreaction in alcohols. The photochemistry of isoalloxazines in alcohols, while somewhat different from the aqueous photochemistry, does not involve a primary photoreduction with the solvent, and photo degradation still dominates. This was an unexpected result and it illustrates the unusual photochemical behavior of isoalloxazines. The anaerobic irradiation of riboflavin in 2‐propanol‐water mixtures showed that the efficiency of photodegradation is linked to the physical properties of the solvent.
ELECTRON TRANSFER FROM PHOTOEXCITED SINGLET AND TRIPLET BACTERIOPHEOPHYTIN—II. THEORETICAL
Authors: Gouterman Martin , Holten Dewey
Published: January 2008

Abstract— A previous paper showed that collision of the first excited singlet state of bacteriopheophytin (Bph*) and p‐benzoquinone (Q) returns Bph* to the ground state; however, excited triplet (Bph+) and quinone on collision produce the radical ions, (Bph+) and (Q−). This paer rationalizes these findings by first estimating the half cell potentials Bph+/Bph* and Bph+/BphT, the energy for the various collision complexes, and the energy of the charge separated ions Bph++ Q− and then estimating the rates for conversion among these various states. Thus it is estimated that the complexes [Bph*Q] or [BphTQ], live ˜5 ps before dissociating. This is long enough for electron transfer to occur, producing the singlet and triplet charge transfer complexes, [Bph+Q−]S or [Bph+Q−]T, either of which could separate to Bph++ Q− in ˜230ps. In the singlet case, quenching by reverse charge transfer [Bph+Q−]S→[Bph Q] occurs more rapidly than ion separation; however, the analogous triplet process, [Bph+Q−]T→ [Bph Q], is spin forbidden, so that ion separation competes successfully with quenching. Spin scrambling, [Bph+Q−]S↔ [Bph+Q−]T, is estimated to be slow, as this explanation requires. In the bacterial photosynthetic reaction center, the initial electron transfer from an excited singlet state of the bacteriochlorophyll dimer complex (BB)* to bacteriopheophytin, giving [(BB+)(Bph−)]S, successfully leads to ion separated species (i) because reverse charge transfer [(BB+)(Bph−)]S→ [(BB)(Bph)] is slowed by a fairly large Franck‐Condon energy, ΔE˜ lev, which is difficult to convert from electronic to vibrational degrees of freedom and (ii) because of the rapid subsequent electron transfer from (Bph+) to another acceptor X.
INTERACTION OF ACRIDINE DRUGS WITH DNA AND NUCLEOTIDES
Authors: Georghiou S.
Published: January 2008

Abstract— At high phosphate‐to‐drug ratios acridine drugs intercalate between hydrogen bonded DNA base pairs causing significant changes in the physico‐chemical properties of DNA. The determination of the nature of the strong (or primary) interaction between acridine drugs and DNA is of great importance for elucidating the mode of the biological action of the drugs.

Nanosecond measurements have revealed a fast depolarization of the fluorescence of proflavine, one of the most extensively studied acridines, bound to DNA. The electronic structure of the complex, however, is not substantially altered during the lifetime of the excited singlet electronic state of the drug. Guanine has been shown to be responsible for the quenching of the proflavine fluorescence upon binding to DNA. A temperature‐jump relaxation study has demonstrated a rather external complexation of this drug with the G‐C base pairs; this complex, whose formation occurs in the strong binding region, is distinct from the weak electrostatic complex.

The findings that the binding ability of a series of acridines correlates with their basicity and that the drug–binding behavior of methylated DNA is significantly different from that of DNA suggested that specific forces may be also involved in the drug–DNA binding in addition to hydrophobic forces. Recent experiments employing molecular complexes of acridines with nucleotides as model systems have provided strong support for the specificity of the drug‐DNA interaction. Hydrogen bonding between the drug and reactive groups of the DNA bases that do not contribute directly to the stability of the helix may be involved in that interaction.

The stoichiometry of the proflavine‐guanosine 5′‐phosphate complex is 1:1. Its association constant increases from 310 M‐1 when proflavine is in its ground electronic state, to 1550 M‐1, when proflavine is in its first excited singlet state. Thus, light absorbed by the drug alters its reactivity which, in turn, results in an appreciable increase in its ability to bind to the nucleotide. In view of the proposed importance of the drug–base interaction in explaining the mutagenic properties of acridine drugs and, in particular, of the proposed involvement of the G‐C base pairs, this finding emphasizes the possible importance of drug photoexcitation in acridine mutagenesis; it also contributes to the elucidation of photodynamic action.

X‐ray diffraction studies have recently provided very interesting demonstrations of strong binding of 9‐aminoacridine and of the phenanthridine drug ethidium bromide to adenine‐uracil base pairs in the crystalline phase.

The ability of photoexcited acridine drugs to inactivate viruses has been recently used for therapeutic purposes. The carcinogenic risk involved, however, is still under investigation.
SPECTROFLUOROMETRIC DETERMINATION OF Mg‐PROTOPORPHYRIN MONOESTER AND LONGER WAVELENGTH METALLOPORPHYRINS IN THE PRESENCE OF Zn‐PROTOPORPHYRIN*
Authors: Smith Barry B. , Rebeiz Constantin A.
Published: January 2008

Abstract. Greening tissues accumulate Mg‐protoporphyrin monoester and a group of metalloporphyrins that exhibit fluorescence emission and excitation properties which are red‐shifted with respect to Mg‐protoporphyrin monoester. These metalloporphyrins are collectively termed longer wavelength metalloporphyrins and are presumed to be metabolic intermediates between Mg‐protoporphyrin monoester (MPE) and protochlorophyllide. The longer wavelength metalloporphyrins, together with Mg‐protoporphyrin monoester, are referred to as the MPE‐equivalent. During the study of the biosynthesis of the components of the MPE‐equivalent and the study of their conversion to protochlorophyllide in vitro, it was observed that Zn‐protoporphyrin and its monoester were also formed. The latter compounds interfered with the determination of the MPE‐equivalent. Simultaneous equations were derived and solved to yield an equation which permitted the determination of the amount of MPE‐equivalent in the presence of Zn‐protoporphyrins from the fluorescence emission spectrum of the mixture. Such determinations were made without prior segregation of the metalloporphyrins.
PHOTOCHEMICAL INTERACTIONS BETWEEN NITROXIDE FREE RADICALS AND PHENOTHIAZINES IN SOLUTION
Authors: Daveloose Denis , Leterrier François
Published: January 2008

Abstract— Ultraviolet irradiation of photosensitive molecules like phenothiazine derivatives leads to the formation of short lived free radicals which are able to reduce stable nitroxide free radicals generally used as spin labels. The measurement of the electron spin resonance signal decay of nitroxides offers a tool for studying the photochemical reaction of phenothiazine derivatives in solution at room temperature, in a 10‐5 to 10‐2M concentration range. Analysis of the reaction mechanism shows that the paramagnetic nitroxide is an efficient quencher of the phenothiazine triplet state; this reaction was used to demonstrate the influence of the solvent, quenching by oxygen and the role of the chemical structure of six phenothiazine derivatives on their photoreactivity in solution.
CHEMILUMINESCENCE DURING PHOTOOXIDATION OF MELANINS AND SOIL HUMIC ACIDS ARISING FROM A SINGLET OXYGEN MECHANISM*
Authors: Slawinski Janusz , Puzyna Wlodzimierz , Slawinska Danuta
Published: January 2008

Abstract— Photooxidation of synthetic melanins and natural soil humic acids in a model system: polymer + OH‐+ O2+ solvent, initiated by irradiation with wavelengths longer than 300 nm, is accompanied by chemiluminescence with the maximum absolute intensity 104− 5 × 105 photons s‐1. Prolonged photoirradiation results in the decrease of both dark and photoinduced EPR signals and decrease of absorption in the spectral range 240–600 nm, indicating destruction of the aromatic core of polymers. Rate of photooxidation and chemiluminescence intensity increases in D2O, in comparison with H2O, by a factor of about 3. Inhibitors of free radicals and O21Δg‐quenchers diminish chemiluminescence by 20–97%. Chemiluminescence spectra measured with cut‐off filters and a calibrated photo‐multiplier operating in the single photon counting mode have emission bands at 480–500, 570 and 615–650 nm. The red band has been assigned to the emission from 2 O2 (1Δg 1Δg) dimols, and the blue‐green band to the sensitized chemiluminescence of fluorescing photooxidation products.
CALCULATED RATES AND EQUILIBRIA OF THERMAL INTERCONVERSION OF TRIPLET (3g‐) AND SINGLET (1Δg and g+) MOLECULAR OXYGEN
Authors: Mendenhall G. David
Published: January 2008

Abstract— From spectroscopic data and rate constants in the literature, equilibrium constants and rates of thermal formation of singlet oxygen (1Δg and 1Σg+) were calculated for a number of conditions. For the gas phase we estimate Keq(1Δg3Σg‐) = 1.67 exp(‐94.31 KJ/RT) and Keq(1Σg+/3Σg‐) = 0.33 exp(‐157.0 KJ/RT). The calculated rate constants for the 3Σg+→1Δg transition of O2 at 25°C varied from 2.5 × 10‐11 s‐1 in water to 4.8 × 10‐16 s‐1 in air, assuming equal solvent interactions with the ground and excited states. Physical quenchers for singlet oxygen are expected to be catalysts for its thermal formation. Equations are presented which allow one to estimate whether such catalysis by quenchers will result in a pro‐oxidant effect.
DETERMINATION OF SINGLET OXYGEN RATE CONSTANTS IN AQUEOUS SOLUTIONS
Authors: Kraljić I. , Sharpatyi V. A.
Published: January 2008

Abstract— A very efficient quenching of singlet oxygen (1O2) by N3‐ ions has been applied to the determination of rate constants of reactions of 1O2 with various substrates (A). This determination has been made possible by choosing experimental conditions which give simple competition between N3‐ and A for 1O2 formed in the steady state irradiation of convenient sensitizing dye (S). The consumption of oxygen by the substrate, as followed with an oxygen analyzer, decreases in the presence of low concentrations of N3‐. Using neutral air saturated aqueous solutions containing the dye phenosafranine + A and varying concentrations of N3‐, the 1O2 rate constants for reactions with biological substrates and some radiation protective agents have been determined.
DETECTION OF SINGLET OXYGEN IN RADIOLYSIS OF AERATED AQUEOUS SOLUTIONS
Authors: Sharpatyi Valery A. , Kraljić Ivan
Published: January 2008

Abstract— The detection of singlet oxygen (1O2) in the γ‐radiolysis of air saturated aqueous solutions may be achieved by using a selective method under such conditions that other strongly reactive intermediates such as −OH radicals do not react or are prevented from giving the same reaction. Since all or most 1O2 acceptors also react with −OH radicals, the elimination of OH radicals with appropriate scavengers may be necessary.

A recently developed method for the detection of 1O2 in neutral aqueous solutions based on the bleaching of p‐nitrosodimethylaniline (RNO) in a solution containing an imidazole derivative, has been used in this work to detect 1O2 in γ‐radiolysis. In the system imidazole + RNO, the reaction between 1O2 and imidazole produces a trans‐annular peroxide which leads to the bleaching of RNO. The bleaching of RNO depends in a characteristic way on the concentration of different imidazole derivatives at high concentrations. This dependence is the same in certain photolysis experiments (where only 1O2 reacts in this way) and in radiolysis. The bleaching of RNO, as induced by the reaction between 1O2 and imidazoles, is also observed in the presence of ethanol which scavenges all −OH radicals but does not react with 1O2 or trans‐annular peroxide. Moreover, in the absence of imidazole, the addition of ethanol to a dilute solution of RNO protects it completely against −OH radical attack. Thus, the results of these experiments indicate that 1O2 may be formed in the radiolysis of air saturated aqueous solutions in a relatively low yield [G(1O2) ∼ 0.1–0.3].
IRRADIATION‐ENHANCED PHYTOCHROME PELLETABILITY IN AVENA: IN VIVO DEVELOPMENT OF A POTENTIAL TO PELLET AND THE ROLE OF Mg2+ IN ITS EXPRESSION IN VITRO
Authors: Quail Peter H.
Published: January 2008

The enhanced phytochrome pelletability that results from in vivo irradiation of Avena shoots may be divided into two operationally defined sequential stages: the in vivo development of a “potential to pellet” and the “expression” of this potential in vitro. Kinetic studies confirm previous findings that the generation of this “potential to pellet” is a very rapid (complete in < 10 s, 25°C), genuinely intracellular process, itself photoreversibly induced by Pfr. In addition, it is shown that the sustained development of the “potential to pellet”, that proceeds in the dark at 0°C following a red pulse, requires Pfr continually in the cell over the entire development period. Far red light immediately terminates further development of the red‐induced “potential” at any point during the development phase. No immediate reduction is observed, however, in that level of “potential pelletability” already attained at the time of the far red pulse. This indicates that the level of “potential pelletability” established in vivo is insensitive to the form of the pigment at extraction regardless of the level reached. “Expression” of the “potential to pellet” refers to the actual detection in homogenates of an enhanced physical association of phytochrome with pelletable material. Maximum “expression” requires the presence of a divalent cation in the medium during homogenization. Rapid posthomogenization addition of Mg2+ to Mg2+‐free extracts sustains enhanced pelletability but with rapidly declining effectiveness over the fmt 1–2 min after extraction. The rate of decline is faster if the phytochrome is present as Pfr than as Pr in the homogenate. Neither these nor previous data permit a distinction to be made between (a) preservation by the cation of a pre‐existing intracellular interaction, and (b) a Mg2+‐mediated induction of an artifactual, in vitro association predetermined in the cell by a genuine phyto‐chrome‐controlled process. Various formalistic models are discussed in the context of these and other data.
PHOTOREACTIVATION OF RNA IN UV‐IRRADIATED INSECT EGGS (SMITTIA SP., CHIRONOMIDAE, DIPTERA) II. EVIDENCE FOR HETEROGENEOUS LIGHT‐DEPENDENT REPAIR ACTIVITIES*
Authors: Kalthoff Klaus , Urban Karl , Jäckle Herbert
Published: January 2008

Abstract. Two biological effects of UV radiation upon Smittia eggs are observed, both of which seem to be associated with the formation of pyrimidine dimers in the RNA (largely ribosomal) of the eggs. While irradiation of the anterior pole region causes the formation of an aberrant segment pattern (double abdomen induction), irradiation of entire eggs leads to an arrest of their development (inactiva‐tion). Both UV effects are photoreversible with different action spectra of the photoreactivating light. A dose rate dependence of the photoreactivation can be observed after both UV effects. The saturating dose rate is about 6 W/m2 (at 440 nm) after UV induction of double abdomens. Upon UV inactivation, the saturating dose rate level for the photoreactivating light is much higher, and a single light flash causes both a considerable biological reactivation and the disappearance of about 7 × 109 pyrimidine dimers from the total RNA per egg. The results indicate the presence of heterogeneous light‐dependent repair activities acting upon UV induced pyrimidine dimers in the RNA of the eggs.
ENERGY TRANSFER VIA PROTEIN‐PROTEIN INTERACTION IN RENILLA BIOLUMINESCENCE
Authors: Ward William W. , Cormier Milton J.
Published: January 2008

Abstract—Radiationless energy transfer is known to play biologically important roles in both photosynthesis and bioluminescence. In photosynthesis, accessory pigments serve as “antennae”, transferring excitation energy into the “reaction centers”. In the bioluminescent coelenterates, energy is transferred from the site of reaction via an accessory protein known as the green‐fluorescent protein (GFP). Coelenterate bioluminescence systems such as that of the sea pansy, Renilla, are well characterized biochemically, and their energy transfer process can be duplicated in vitro using isolated and purified components. We have measured efficient in vitro energy transfer from the electronic excited state of the enzyme‐bound oxyluciferin to the green‐fluorescent protein at protein concentrations of 0.1 μM. We have also demonstrated a 1:l complex between these proteins, under conditions of energy transfer, by the chromato‐graphic technique of Hummel and Dreyer. These observations indicate that bioluminescent energy transfer is mediated via protein‐protein interaction. Furthermore, with inter‐species cross‐reaction studies and protein modification techniques we have shown that the interaction between luciferase and GFP is highly specific. These features make the Renilla system an attractive alternative to the photosynthetic systems as a tool for studying radiationless energy transfer.
INTERACTION OF 9‐AMINOACRIDINE WITH 7‐METHYLGUANOSINE AND 1,N6‐ETHENOADENOSINE MONOPHOSPHATE
Authors: Kubota Yukio , Nakamura Hiroki , Morishita Mayumi , Fujisaki Yasuo
Published: January 2008

Abstract—Fluorescence properties of 9‐aminoacridine in aqueous solutions of 7‐methylguanosine (7MeG) and 1,N6‐ethenoadenosine monophosphate (εAMP) have been examined. It was found that fluorescence of the dye was quenched by 7MeG and εAMP as well as by unmodified nucleotides such as GMP and AMP. Quantitative analysis of the results shows that both dynamic and static quenching processes are responsible for the quenching of fluorescence.
IDENTIFICATION OF TRYPTIC CHROMOPEPTIDES OF PHYTOCHROME ON SODIUM DODECYL SULFATE GELS: IMPLICATIONS FOR STRUCTURE
Authors: Stoker Blanche M. , McEntire Kerry , Roux Stanley J.
Published: January 2008

Abstract— After electrophoresis on sodium dodecyl sulfate polyacrylamide gels, bleached chromopeptides of phytochrome can have their blue color restored by soaking the gels in 20% trichloroacetic acid. The blue bands have a broad absorption maximum between 630 and 655 nm, characteristic of denatured phytochrome. The restored color retains most of its intensity for up to 2 h, but gradually bleaches again until it disappears completely within 24 h. This visualization method is used to identify the number and sizes of phytochrome chromopeptides produced by limited tryptic digestion. The results reveal some structural requirements for photoreversibility and are consistent with a model of phytochrome structure that predicts a high degree of symmetry within the native subunit.
THE MECHANISM OF THE 9,10‐DIBROMOANTHRACENE MEDIATED TRIPLET‐SINGLET ENERGY TRANSFER IN THE TETRAMETHYL‐1,2‐DIOXETANE ENERGIZED RUBRENE LUMINESCENCE*
Authors: Adam Waldemar , Cancio Edith M. , Rodriguez Osvaldo
Published: January 2008

Abstract— The ternary chemiluminescent system consisting of tetramethyl‐dioxetane (TMD), 9,10‐dibromoanthracene (DBA) and rubrene (Ru) has been investigated in benzene solution and in polystyrene matrices. DBA has been found to mediate the energy transfer between excited triplet acetone (3K), generated from TMD, and rubrene resulting in the enhancement of the Ru emission and reduction in the DBA emission. A detailed kinetic analysis confirms that ca. 50% of the enhanced chemilumines‐cence involves triplet‐singlet (TS) energy transfer from 3K to DBA, followed by singlet‐singlet (SS) energy transfer from DBA to Ru, the remainder ca. 50% being due to reabsorption of DBA fluorescence by rubrene. It is concluded that the TS energy transfer is of the resonance type, occurring with a rate of kTSK.DBA= (1.4 ± 0.4) ± 109M‐1s‐1 and an efficiency of øTSK.DBA= 0.3 ± 0.1. As expected, the SS energy transfer is also of the resonance type, taking place at comparable rates in benzene solution and in polystyrene matrices, is. kSSDBARU= 1.5 ± 1010 M‐1 and (2.2 ± 0.2) ± 1010M‐1s‐1, respectively.
VARIATION IN THE RATES OF SYNTHESIS AND DEGRADATION OF PHYTOCHROME IN COTYLEDONS OF CUCURBITA PEPO L. DURING SEEDLING DEVELOPMENT
Authors: Schäfer E.
Published: January 2008

Abstract— The time courses for Pr appearance, Pr disappearance and Pfr destruction have been analysed in cotyledons of Cucurbita pepo L. after different preirradiation programs. In etiolated seedlings the rate of Pr appearance is low in young seedlings reaching a maximum in 3.5–5 day old seedlings then decreasing rapidly with increasing age. The rate of Pfr destruction is very low in young seedlings, increases rapidly up to the 4th day and then remains almost constant. The disappearance of Pr becomes significant for seedlings older than 45 days. These reactions seem not to be influenced by short preirradiations. However, after prolonged preirradiation, a degree of control of P, appearance and/or disappearance by the “internal clock appears to be operative.
PROPERTIES OF THE RETINAL BINDING SITE IN BACTERIORHODOPSIN. USE OF RETINOL AND RETINYL MOIETIES AS FLUORESCENT PROBES
Authors: Schreckenbach Thomas , Walckhoff Bärbel , Oesterhelt Dieter
Published: January 2008

Abstract— The fluorescence spectra of various reduced bacteriorhodopsin chromophore species indicate energy transfer from aromatic amino acid side chains of the protein to the retinyl moiety. Binding studies with retinol reveal that energy transfer occurs only when the retinyl moiety is bound in the chromophoric site of the protein. Retroretinol is a fluorescent probe for the binding site.
CORRELATION BETWEEN ABSORBANCE CHANGES AND A PHYSIOLOGICAL RESPONSE INDUCED BY BLUE LIGHT IN NEUROSPORA
Authors: Klemm Eva , Ninnemann Helga
Published: January 2008

Abstract— Absorbance changes due to the photoreduction of a b‐type cytochrome are associated with many biological blue light‐controlled processes. Evidence is presented for their causal relationship with the perception of light which induced conidia formation under conditions of starvation in Neurospora crassa mutant albino band, but not with light‐induced phase shifts of conidiation bands.
THE IMPORTANCE OF COMPLEX FORMATION IN THE SENSITIZATION OF Eu(III) EMISSION BY OROTIC ACID
Authors: Sarpotdar Arvind , Burr John G.
Published: January 2008

Abstract— Orotic acid (I) and 3‐methylorotic acid (II) are the only orotic acid derivitives which efficiently sensitire emission from Eu(III) in D2O solution. This emission is only weakly sensitized by I‐methylorotic acid (III), 1,3‐dimethylorotic acid (IV), the methyl and isopropyl esters of orotic acid (V) 6‐acetyluracil (VI) and not sensitized at all by the bases uracil. thymine and their nucleosides. Substituent groups on either the carboxyl group or the N‐l position of the ring thus prevent efficient energy transfer from the excited orotic acid to Eu(III). These structural requirements for efficient energy transfer are the same as the structural requirements for formation of a stable. bidentate. ground state complex between Eu(III) and orotic acid (VII) (Sarpotdar and Burr, 1978).

We, therefore, propose that sensitization of Eu(III) emission by orotic acid at pH 5 is an example of energy transfer within the bidentate complex of Eu(III) and orotic acid. We also propose that the complexed orotic acid is itself excited by eollisional energy transfer from free triplet excited orotic acid (since the concentration of complex measured to be present. 5–7%, is too low to account for the efficiency of the sensitization). We also propose that emission from the excited complexed Eu(III) can be either from the complexed ion or from free Eu(III)* resulting from dissociation of the complex during the lifetime of the excited ion.

The efficiency of Eu(III) sensitized emission is shown to depend on the concentrations of Eu(III). orotic acid and pH with relationships kinetically consistent with the above hypothesis.
A BIOCHEMICAL SCREENING TEST FOR THE PHOTOSENSITIZING POTENTIAL OF DRUGS AND DISINFECTANTS
Authors: Schothorst A. A. , Suurmond D. , Lijster A. de
Published: January 2008

Abstract— A series of photosensitizers known to cause photodermatitis were tested with respect to photosensitizing properties. Irradiation of these sensitizers together with unsaturated fatty acids or amino acids showed that few of them can be transformed by most of the photosensitizers. SH groups can. however, be destroyed by most of the photosensitizers known in dermatological practice. At low photosensitizer‐to‐SH group ratios, GSSG is formed; at higher ratios, other transformations of GSH predominates. The reactivity of GSH with ninhydrin is decreased after irradiation with a photo‐sensitizer. Glutathione seems to be a biomolecule that is suitably sensitive to photosensitized modification and thus suitable for evaluation of any photosensitizing activity that new drugs may have as an unwanted side effect.
THE POSSIBLE PRESENCE OF A THIRD INTERMEDIATE FOR IODOPSIN AT ‐195°C*
Authors: Gupta B. D. , Goyal I. C.
Published: January 2008

Abstract— From the theoretical analysis of the time variation of the change in absorbance of chicken iodopsin solution (at—195°C), the formation of a new intermediate during bleaching has been suggested.
NITRATE REDUCTASE—A KEY ENZYME IN BLUE LIGHT‐PROMOTED CONIDIATION AND ABSORBANCE CHANGE OF NEUROSPORA
Authors: Klemm Eva , Ninnemann Helga
Published: January 2008

Abstract— Neurospora, when starved for several hours, can be stimulated by blue light to conidiate and also shows a blue light‐inducible, flavin‐mediated absorbance change near 425 nm due to photoreduc‐tion of a h‐type cytochrome. Under the same physiological conditions, nitrate reductase activity (NADPH‐dependent nitrate reduction) decreases and the activity of its small subunit (methylviologen‐to‐nitrate reductase activity) increases. The increased activity is membrane associated (plasma membrane and mitochondria). The methylviologen‐to‐nitrate activity increase can also be brought about by treating mycelium briefly with diluted acetone. It is, therefore, interpreted as change within the nitrate reductase molecule (configuration change or separation of subunits with changed exposure of active sites). After acetone treatment the blue light‐induced absorbance change can be observed immediately in the mycelium. Nitrate reductase with its flavin and protoheme prosthetic groups seems to be involved in both events, the induction of conidiation and in the described absorbance change.