COOPERATION OF QUERCETIN WITH ASCORBATE IN THE PROTECTION OF PHOTOSENSITIZED LYSIS OF HUMAN ERYTHROCYTES IN THE PRESENCE OF HEMATOPORPHYRIN

Abstract— Quercetin(20–100 μ M ) suppressed photohemolysis sensitized by hematoporphyrin, while ascorbate(10–100 μ M ) stimulated it. However, in the presence of 40 μ M quercetin, ascorbate promoted the suppression. The suppression by quercetin was due to scavenging of both singlet oxygen generated by a photosensitized reaction and radicals generated by decomposition of lipid peroxides formed by a singlet oxygen-dependent reaction. In scavenging, quercetin was oxidized and the oxidation was suppressed by ascorbate. Ascorbate was oxidized by illumination in the presence of quercetin. It is suggested that the cooperation of quercetin with ascorbate in photohemolysis is due to reduction of oxidized quercetin by ascorbate regenerating the flavonol.     

EFFECTS OF HEMATOPORPHYRIN DERIVATIVE ON THE CELLULAR ENERGY METABOLISM IN THE ABSENCE AND PRESENCE OF LIGHT

Effects of Photofrin II on energy metabolism and metabolic viability were studied in a mammalian transformed cell line (BHK-21) in dark and after photo-irradiation with visible light. Cells were allowed to accumulate Photofrin by incubating for 4 h in buffer containing Photofrin (5-60 micrograms/ml). The results show that Photofrin significantly affects the cellular energy metabolism even in the absence of light; activity of cytochrome c oxidase is decreased and glucose utilization and lactate production (glycolysis) are increased. Irradiation with light resulted in a significant decrease in the activity of cytochrome c oxidase, glycolysis, ATP content, energy charge, ratios of adenine nucleotides like ATP/ADP, ATP/AMP and cell viability (dye exclusion test). Presence of inhibitors of energy metabolism, potassium cyanide (respiration) and 2-deoxyglucose (glycolysis), further enhanced the cytotoxic effects induced by hematoporphyrin derivative and light.     

THE ROLE OF O2- IN THE CHEMILUMINESCENCE OF LUMINOL*

Abstract— The chemiluminescence of luminol in buffered aqueous solutions is inhibited by superoxide dismutase. This occurs whether the luminescence is induced by ferricyanide, persulfate, hypochlorite, or by the action of xanthine oxidase on xanthine. Since superoxide dismutase inhibits reactions which involve O₂^-, we conclude that this radical is a constant factor in the chemiluminescence of luminol in aqueous solutions. The kinetics of light production are discussed in terms of hypothetical mechanisms that fit the available data. The strong luminescence of luminol in aprotic solvents or in aqueous systems containing relatively high concentrations of H₂O₂ could not be explored in this way, because superoxide dismutase is inactive under such conditions.     

THE EFFECTS OF NEAR-UV RADIATION ON HUMAN LENS β-CRYSTALLINS: PROTEIN STRUCTURAL CHANGES and THE PRODUCTION OF O2_ and H2O2

beta-Crystallins (beta 1-, beta 2- and beta 3-crystallin) comprise nearly half the protein of the human lens. The effect of near-UV radiation, which is one of the possible risk factors in cataract formation, on the beta-crystallins is investigated in this study. Protein intersubunit crosslinking, change in charge of the protein subunits to more acidic species and changes in protein tertiary structure (conformation) by 300 nm irradiation are reported. The fluorescence yield of protein tryptophan residues decreases by 300 nm irradiation. There is an increase in nontryptophan fluorescence (lambda cx 340 nm, lambda cm 400-600 nm), and in protein absorption at 340 nm, due to the formation of tryptophan photooxidation products. Both tryptophan and its oxidation products can be photoexcited by 300 nm irradiation and the latter are known to be good photosensitizers. The results provide evidence for the generation of H2O2 in the irradiated human beta-crystallin solutions by the Type I photosensitizing action of the chromophores absorbing at 300 nm. The H2O2 is generated via the intermediate production of O2 anion; the latter spontaneously dismutates to H2O2, presumably via O2- protein interactions. The amount of H2O2 generated per absorbed photon is compared for various solutions of beta 1-, beta 2- and beta 3-crystallins from human lenses of different age.     

SIMPLE EXPLANATION OF THE MISSES IN THE COOPERATION OF CHARGES IN PHOTOSYNTHETIC O2 EVOLUTION

Abstract —In the model of Forbush et at. (1971) the observed damping of the flash yield sequence of photosynthetic O₂ evolution was related to a certain percentage of ‘misses’ (α; i.e. centers not converted). The possibility of a miss was supposed to be equal for all states S_0.1,2,3. We propose a new model and a new recurrence law that gives better quantitative agreement with the O₂ yield oscillations observed in Chlorella during a sequence of flashes. We find a better fit with all experimental results by assuming very unequal misses; the misses occur nearly exclusively on S₂ (and also sometimes on S₃). In the simpler case of only one miss on one state, half of S₂ exists as an inactive form S₂₊^- because it is in apparent equilibrium with pool A. The active form of S₂ is converted to S₃ in a flash and the unchanged inactive form S₂₊^- explains the miss: S ₁ hv→S₂₊^-=S₂hv→S₃ (S₂₊^- is a transition state between S₁ to S₂ associated with Q^-). In the dark, the apparent equilibrium constant K_A between pool A and Q (i.e. S₀, S₁ in the dark) is very large; this explains why there is no miss on these states. In light, the experimental value of K_A between pool A and Q (i.e. S₂, S₃ in the light) is 1, and this explains why the misses are large for states S₂, S₃; i.e., S₂₊^-/S2- 1 and sometimes S₃₊^-/S₃?0–1. This new model predicts that the total number of active states ΣS_i=S₀+S₁+S₂+S₃ is an oscillating function of the flash number. This sum 2S, is also the number of trapping centers for excitons. As fluorescence is proportional to excitons that are not trapped, our model explains why the fluorescence oscillates as a function of the flash number. We find also that the initial rates of O₂ evolution after (n - 1) flashes vs the 02 yield of the n^th flash are not exactly on a straight line, which also favors our model.     

INFLUENCE OF THE PEPTIDE BOND ON THE SINGLET MOLECULAR OXYGEN-MEDIATED (O2[g]) PHOTOOXIDATION OF HISTIDINE and METHIONINE DIPEPTIDES. A KINETIC STUDY

The dye-sensitized photooxidation of l -histidine (His) and l -methionine (Met) and their simplest dipeptides with glycine (Gly) (His-Gly, Gly-His, Gly-Met) and Met-methyl ester (Met-ME) mediated by singlet molecular oxygen (O₂[_g]) was studied. The overall rate constants in acetonitrile-H₂O (K_t) for O₂(¹_g) quenching were measured by time-resolved phosphorescence detection. In H₂O a competitive kinetic method was employed. In both solvents the reactive rate constants (K_t,) were determined to discriminate between the overall and physical contributions to the quenching. The kinetic and mechanistic aspects of the interaction are discussed. For His-Gly, the peptide bond has practically no effect on the kinetics of photooxidation. For Gly-His the overall rate constant is much higher than that for His and His-Gly, in both H₂O and acetonitrile-H₂O. The main contribution to k₁ (for Gly-His) is the physical quenching of O₂(¹_g)- In water the k_t/k_r ratio for free His and His-Gly is 1.0, reaching a value of 2.0 in the organic solvent-H₂O mixture. The rates of-NH₂ loss upon sensitized photooxidation in all cases parallel the trend of k_r values. The main results for the His series indicate that: (1) a polar environment favors autoprotection (i.e. an increase in the contribution of physical quenching) against photodynamic effects; (2) only the rate constant for reactive interaction with O₂[_g] does not depend on the location of the peptide bond involving His. For Met derivatives the k_t, values are higher in both solvents than that for free Met. Only for the free amino acid in H₂O is the interaction with O₂(¹_g) totally reactive. For Gly-Met and Met-ME the physical quenching prevails: k_t, is, in both solvents, about one order of magnitude higher than k_r. According to our results on -NH₂ loss and on the basis of previous investigations by others, the photooxidative products distribution in the Met series indicates that Gly-Met yields only dehydroMet, whereas Met and Met-ME produce a mixture of Met-sulfoxide and the Met-dehydro compound.     

SEARCH FOR SINGLET OXYGEN LUMINESCENCE IN THE DISPROPORTIONATION OF HO2/O2

Abstract— During the reaction HO₂+ HO₂ (or O₂^-) = H₂O₂+ O₂ in aqueous solution, no luminescence in the region 620–720 nm, expected if the product O₂ were formed in a singlet state, could be detected. If any singlet O₂ is formed, its yield must be less than 10%. Faint luminescence, sometimes found at shorter wavelengths, was shown to arise from reaction of HO₂ with impurities in the reagents present.     

PHOTOINACTIVATION OF A Chlamydomonas MUTANT(NL–11) IN THE PRESENCE OF METHIONINE: ROLES OF H2O2 and O-2

Abstract— A mutant of Chlamydomonas reinhardtii (NL–11) isolated from a wild type (137c+) was inactivated in the light in the presence of methionine at concentrations where the wild type was not inactivated. The inactivation was suppressed by either catalase or superoxide dismutase (SOD). Light-induced H₂O₂ formation and nitroblue tetrazolium (NBT) reduction inNL–11 were greater than those in the wild type. Methionine stimulated both the H₂O₂ formation and the NBT reduction inNL–11 as well as the wild type. The light-induced NBT reduction inNL–11 in the presence of methionine was partially suppressed by externally added SOD suggesting the participation of O^-₂. These results suggest that the hypersensitivity ofNL–11 to methionine in the light is due to stimulated formation of H₂O₂ and O^-₂.     

STUDIES ON FLAVINS IN ORGANIC SOLVENTS—II*. PHOTODECOMPOSITION OF RIBOFLAVIN IN THE PRESENCE OF OXYGEN

Abstract— The photodegradation of riboflavin by 436 mμ monochromatic light and of lumichrome by white nonfiltered light was studied in a set of organic solvents including ethanol, acetone, dioxane, pyridine and acetic acid. For comparison, water was used as a solvent. Photolysis was carried out in the presence of atmospheric oxygen. Riboflavin and lumichrome were found to be effectively stabilized towards the action of light by hydrogen bonds with solvent molecules, and consequently are most light-stable in water solutions. The overall scheme of riboflavin photolysis in organic solvents seems to be the same as in aqueous solutions. Lumichrome has been found as the main product of riboflavin photolysis in the organic solvents tested.     

MOLECULAR CHANGES DURING THE PHOTOOXIDATION OF α-CRYSTALLIN IN THE PRESENCE OF UROPORPHYRIN

Singlet oxygen reacts preferentially with three amino acids in proteins, His, Trp and Met. In order to study the specific molecular events that result from such oxidations, calf a-crystallin was photooxidized in the presence of uroporphyrin and the reactions were investigated by high performance liquid chromatography peptide mapping using a photodiode array detector followed by fast atom bombardment mass spectrometry (FAB-MS). From these studies, the following conclusions can be inferred: (1) Upon photooxidation residue Met-68 of the B chain is oxidized to Met sulfoxide, whereas residue Trp-60 remains intact. (2) Two of the 16 His residues in a-crystallin are photooxidized with an apparent pK_a of ca 7.0. (3) FAB-MS analysis suggests that residue Lys-166 close to the C-terminal end of the A chain forms a cross-link with the His-7 residue close to the N-terminal end of the A chain. This may be either an inter- or intramolecular cross-link.     

TYPE I AND TYPE II MECHANISMS IN THE PHOTOOXIDATION OF L-TRYPTOPHAN AND TRYPTAMINE SENSITIZED BY HEMATOPORPHYRIN IN THE PRESENCE AND ABSENCE OF SODIUM DODECYL SULPHATE MICELLES

Abstract— Oxygenated aqueous solutions (pH 10) of L-tryptophan or tryptamine containing hematopor-phyrin and/or specific quenchers of the possible reactive intermediates were irradiated with visible light in the presence and in the absence of dispersions of sodium dodecyl sulphate micelles. The rate of loss of the indole derivatives was followed over several min. In the absence of dispersed micelles, indole derivatives appeared to be photooxidized largely by a type I mechanism involving electron transfer from triplet hematoporphyrin to the indole moiety. A type II (^lO₂-involving) mechanism was of minor importance. The presence of sodium dodecyl sulphate micelles, where the porphyrin was solubilized in a monomeric state, exerted only a slight influence on the competition between the two reaction pathways described above in the case of tryptophan, which was essentially all present in the aqueous phase. On the other hand, tryptamine, when dissolved within micelles, underwent photooxidative attack exclusively by ¹O₂ which was generated within a micelle, diffused through the aqueous phase and penetrated into another (tryptamine-containing) micelle; the reduced efficiency of the latter photoprocess was probably a consequence of the low probability of ¹O₂ penetration into charged micelles.     

REEVALUATION OF THE SPECTRAL AND KINETIC PROPERTIES OF HO2 AND O2- FREE RADICALS

Abstract— The spectra and molar absorbances of the HO₂ and O₂^- free radicals have been redetermined in aqueous formate solutions by pulse and stopped-flow radiolysis as well as by ⁶⁰Co gamma-ray studies. The extinction coefficients at the corresponding maxima and 23°C are ²²⁵= 1400 ± 80 M ^-1 cm^-1 and ²²⁵= 2350 ± 120 M ^-1 cm^-1 respectively. Reevaluation of earlier published rate data in terms of the new extinction coefficients yielded the following rate constants for the spontaneous decay of HO₂ and O₂^-: K _Ho2+HO2= (8.60 ± 0.62) × 10⁵ M ^-1 s^-1; K _Ho2+O2-= (1.02 ± 0.49) × 10⁸ M ^-1 s^-1; K _Ho2+O2- < 0.35 M ^-1 s^-1. For the equilibrium HO₂→ O₂^-+ H⁺ the dissociation constant is K _Ho2= (2.05 ± 0.39) × 10^-5 M or p K _HO2= 4.69 ± 0.08. G (O₂^-) has been evaluated as a function of formate concentration.     

RADIATION ACTIVATION OF CARCINOGENS AND THE ROLE OF OH AND O2-

Abstract— Radiation-induced covalent binding of labelled carcinogens to DNA has been investigated under a variety of conditions using ultrafiltration or millipore filtration of TCA precipitable complexes. High yields of carcinogen binding at high DNA concentrations are also observed for a variety of small molecules and are not carcinogen-specific. At high carcinogen concentrations, radiation-induced unstable electrophilic carcinogenic species are produced, and undergo free-radical reactions which simulate cellular redox reactions involved in metabolic carcinogen activation, leading to the formation of covalently bound carcinogen adducts to DNA as a potential target macromolecule. The yields of carcinogen-DNA adducts increase linearly with dose and depend upon carcinogen concentration. The results of scavenger studies indicate that the oxidising species O₂^- and OH are the principal activating species. Rate constants for the selective radiation-induced oxidation reactions of various chemical carcinogens with superoxide have been measured by a competition kinetic method using pulse radiolysis. The relatively long-lived superoxide radical reacts with carcinogens at a rate which is two orders of magnitude slower than the diffusion-controlled rate for the hydroxyl radical, thus allowing a measure of O₂^- specificity in the presence of competing reactants within the cell.     

THE STIMULATING EFFECT OF A COLD, DARK PRETREATMENT ON THE ETIOPLAST/CHLOROPLAST TRANSFORMATION OF ANGIOSPERMS–II. SYNERGISM BETWEEN RED-LIGHT and COLD PRETREATMENT ON THE CO2- and O2-GAS-EXCHANGE OF WHEAT LEAVES

Abstract— Recently we reported on the stimulating effect of a cold, dark pretreatment on the processes of greening of dark-grown angiosperms under continuous white light (Schönbohm et al., 1988; Physiol. Plant. 72 ,541–546). These effects could be nullified by a subsequent second dark phase (25°C) which precedes the white light period. Our analysis was now focused on the effect of cold, dark pretreatments (with or without red-preirradiation) on the gas exchange (O₂; CO₂) of etiolated primary leaves of wheat during a subsequent white light period. The following results were obtained: (1) The net-O₂-consumption under continuous white light decreased much more quickly after a cold than after a warm pretreatment. (2) This effect was enhanced by red-preirradiation. (3) The O₂-compensation point was reached more quickly during the de-etiolation period when the leaves had been subjected to a cold instead to a warm pretreatment. (4) The “cold-effect” could be nullified by a subsequent warm, dark pretreatment (in this material the compensation point could not be reached within 8 h). (5) Cold treated material which had also been exposed to red light showed during the first 30 min of de-etiolation an extremely strong ^“out-burst” of CO₂. No correlation was apparent between the O₂-uptake and this high CO₂-release. (6) A cold, dark pretreatment induces a decrease of CO₂-release during the second half of the de-etiolation period. This effect could be nullified by a secondary warm, dark treatment given after the cold, dark pretreatment. Our experiments indicate that red-preirradiation and cold, dark pretreatment stimulate chlorophyll synthesis (Schonbohm et al., 1988) and also photosynthetic O₂-evolution and CO₂-uptake. We also assume that this pretreatment causes CO₂ release that is neither directly related to the respiratory electron transport chain nor to the photorespiration.     

苯甲醛及其衍生物对铈离子存在下丙烯酰胺聚合的影响

<正> 虽然Santappa等早已报道Ce~(4+)(高氯酸铈)/甲醛体系能引发丙烯腈(AN)、甲基丙烯酸甲酯(MMA)的聚合,但对醛的活性以及参与引发单体聚合的自由基都未有详细报道,近来孙燕慧等发现脂肪醛能显著促进Ce~(4+)(硝酸铈铵CAN)引发丙烯酰胺(AAM)的聚合,而且醛的活性远大于相应的醇。至于芳香醛对于Ce~(4+)引发烯类单体的聚合的影响也未见详细报道。本文扼要报道苯甲醛(BA)及其衍生物对-硝基苯甲醛(PNBA)、间-硝基苯甲醛(MNBA)、间-溴苯甲醛(MBBA)、对-氯苯甲醛(PCBA)对Ce~(4+)(CAN)存在下丙烯酰胺聚合的影响,测定了其聚合速率,以UV吸收光谱、ESR波谱测定     

PHOTOOXYGENATION OF 3-HYDROXYFLAVONE IN A 12 K O2 MATRIX

Abstract— We present an infrared study of 3-hydroxyflavone in 12 K Ar and O₂ matrices. Although it is extremely photostable in an Ar matrix, a remarkable oxygenation reaction for 3-hydroxyflavone takes place upon photoexcitation in an O₂ matrix. The primary photoproduct is concluded to be a keto-hydroperoxide. On further photolysis the keto-hydroperoxide affords the photostable secondary product 2-(benzoyloxyl)benzoic acid, as well as CO and CO₂ through two independent pathways.     

RADIATION DEGRADATION OF CHITOSAN IN THE PRESENCE OF H2O2

INTRODUCTIONChitosan, poly-β-(1 -?4)-D-glucosamine, can be obtained from chitin by deacetylation with alkali. It is soluble indilute acidic medium due to the presence of amino groups. The use of chitosan in many areas, such as foodprocessing, biochemistry, Pharmaceuticals, medicine, and agriculture has been developed over the pastdecades[1,2].In recent years, it has been reported that many properties of chitosan depend on the molecular weight[3]. Thechitosan oligomers possess better fun…     

ELIMINATION OF THE EFFECT OF CONTAMINATING CO2 IN THE 18O-LABELING OF THE CO2 PRODUCED IN BIOLUMINESCENT REACTIONS

Abstract— Although the mechanism of bioluminescent reactions in various species, such as fireflies, ostracod crustaceans ( Cypridina ), sea pansies ( Renilla ), and the deep-sea shrimp Oplophorus , are thought to involve dioxetanone intermediates, studies reported in the past from different laboratories have included widely different experimental results, most likely due to various factors including the effects of contaminating CO₂. With the improved technique employed in the present study, bioluminescent reactions of the firefly and Cypridina in ¹⁸O₂ gas resulted in an incorporation of over 75% of ¹⁸O into one oxygen of the product CO₂. with a reproducibility within a few per cent. When ¹³CO₂. instead of the product CO₂ of the bioluminescent reaction, was studied in an H₂¹⁸O medium, the exchange of one oxygen of ¹³CO₂ with H₂O was 64%. and the effect of contaminant CO₂ amounted to 1418% of the total CO₂. These results suggest that every molecule of CO₂ formed in the bioluminescent reactions of the firefly and Cypridina had intially contained 1 oxygen atom derived from O₂.     

EFFECT OF TEMPERATURE AND pH ON THE QUENCHING OF TRIPLET LUMIFLAVIN IN THE PRESENCE AND ABSENCE OF FERRI- AND FERROCYANIDE

Abstract— –Flash photolysis at 450 nm over the temperature range 0.8–60°C was used to determine Arrhenius parameters for the first and second order disappearance of triplet lumiflavin (1.66 µ .M ) at a flash energy of 2 kj in deaerated phosphate buffer at varying pH:
³Lf → Lf₀
³Lf +³Lf → Lf₀+ Lf₀
Arrhenius parameters were also determined for the pseudo first-order quenching of triplet lumiflavin by 10 µ M ferri- and ferrocyanide ions,
³Lf + Fe³⁺→ Fe³⁺→ Lf₀+ Fe³⁺ (energy transfer)
³Lf + Fe²⁺→ Lf^-+ Fe³⁺ (electron transfer)
and for disappearance of the semireduced lumiflavin in the presence of ferrocyanide at pH 6.8, by the second-order reaction
Lf^-+Lf ^-→ Lf₀+ Lf⁼.