Photochemistry and Photobiology
1751-1097
0031-8655
Mỹ
Cơ quản chủ quản: WILEY , Wiley-Blackwell
Lĩnh vực:
Medicine (miscellaneous)RadiationPhysical and Theoretical ChemistryBiochemistry
Các bài báo tiêu biểu
REGULATION OF THE PHOTOSYNTHETIC LIGHT REACTIONS BY THE BIOLOGICAL CLOCK
Tập 40 Số 6 - Trang 789-794 - 1984
HETEROGENEITY OF THE PHOTOCHEMICAL CENTERS IN SYSTEM II OF CHLOROPLASTS* Abstract— In 3‐(3,4‐dichlorophenyl)‐1,1‐dimethylurea (DCMU) poisoned chloroplasts of algae and‘ higher plants the area over the fluorescence induction curve increases with biphasic first order kinetics (Melis and Homann, 1975). Two possibilities are considered to explain the biphasic nature of the area growth. The first is a sequential double reduction of the primary electron acceptor in system II while the second envisages a heterogeneity of its photochemical centers. The kinetic properties of the area growth after firing a single saturating flash proved to be incompatible with the predictions of the “sequential double reduction” model. This conclusion was corroborated by results obtained from a kinetic analysis of the area restoration process in the dark, and an analysis of the partially restored areas.Assuming an existence of a heterogeneous pool of photochemical centers, the growth of the area over the fluorescence curve could be further analyzed to yield two components, a fast a‐component, and a relatively slow β‐component. The kinetic characteristics of these components, and the effect of a short saturating flash on their respective size, led to the conclusion that one type of photochemical center had a faster recombination rate of the photochemically separated charges and was less efficient in trapping excitation energy.
Tập 23 Số 5 - Trang 343-350 - 1976
<i>IN VIVO</i> CHLOROPHYLL <i>a</i> FLUORESCENCE TRANSIENTS AND THE CIRCADIAN RHYTHM OF PHOTOSYNTHESIS IN <i>GONYAULAX POLYEDRA</i> Abstract— The intensity of chlorophyll a fluorescence during the early part of fluorescence induction at O , initial fluorescence, and P, peak fluorescence, was higher during the day phase of the circadian cycle than during the night phase in continuous light (LL) conditions and was positively correlated with the rate of oxygen evolution. The circadian rhythm in fluorescence in LL persisted in the presence of 10μM 3–(3,4‐dichlorophenyl)‐1,1‐dimethylurea (DCMU), which blocks electron flow from photo‐system (PS) II in photosynthesis. The rhythmic changes in fluorescence intensity are consistent with a lower rate constant for radiationless transitions during the day phase than during the night phase of the circadian rhythmicity. The circadian changes in the intensity of fluorescence were abolished at 77K, which may indicate the importance of structural changes in membranes in circadian oscillations.
Tập 30 Số 2 - Trang 309-311 - 1979
PHOTOSYSTEM II HETEROGENEITY IN THE MARINE DIATOM <i>Phaeodactylum tricornutum</i> Abstract— The kinetics of photosystem II photochemistry are analyzed in the marine diatom Phaeodacfylum tricornutum by measurement of fluorescence induction in cell suspensions treated with 3–(3,4‐dichlorophenyl)‐1,1‐dimethylurea. Photosystem II kinetics are found to be biphasic, the sum of two exponential components, suggesting that biphasic energy conversion in photosystem II may be a general consequence of thylakoid membrane appression. The emission wavelength‐dependence of fluorescence induction suggests that the two photosystem II components have different variable fluorescence emission spectra. The slower component exhibits characteristic emission of the diatom light‐harvesting complexes while emission from the faster component resembles that of the photosystem II reaction center. Variable fluorescence emission (293 K) at wavelengths > 700 nm is assigned to photosystem II. Application of model equations indicates that the two photosystem II unit types differ primarily in antenna size. A new analytical procedure is presented which eliminates ambiguities in the kinetic analysis associated with the incorrect assignment of the maximal fluorescence yield.
Tập 43 Số 5 - Trang 535-544 - 1986
KINETIC ANALYSIS OF THE FLUORESCENCE INDUCTION IN 3‐(3,4‐DICHLOROPHENYL)‐1,1‐DIMETHYLUREA POISONED CHLOROPLASTS Abstract— The size of the area over the fluorescence rise curve of chloroplasts is a measure of the total number of quanta utilized in photosystem II during the fluorescence induction, while the growth of the area reflects the progress of photochemical events. In the presence of 3‐(3,4‐dichlorophenyl)‐1,1‐dimethylurea (DCMU), the growth kinetics of the area are affected by the reoxidation of the primary acceptor Q ‐ with stored oxidizing charges on the donor side of system II.At low light intensities, a slow component of this back reaction may limit the steady state fluorescence emission. At higher intensities, however, the fluorescence rise is limited solely by photochemical events, although fast thermochemical reactions like the immediate recombination of photochemically separated charges may affect the efficiency of the photochemistry. A kinetic analysis of the area growth at moderate light intensities revealed that it occurred in two first order phases which were described by the rate constants k α and k β . The biphasic nature suggested a sequential two‐electron reduction of the primary acceptor Q , or the presence of two different types of photochemical centers in system II. The rate constants were light intensity dependent. They also were affected by changes in pH, by an addition of NH2 OH, or by a preillumination with short flashes prior to addition of DCMU. It is suggested that the pH of the medium, the presence of NH2 OH, and the flash induced state Sn of the water splitting enzyme, control the values of k α and k β by changing the rate constants of electron carrier interactions in the reaction center complex, with a resulting modification of the frequency of back reactions between the primary donor and the primary acceptor.
Tập 21 Số 6 - Trang 431-437 - 1975
THE PHOTODEGRADATION OF PORPHYRINS IN CELLS CAN BE USED TO ESTIMATE THE LIFETIME OF SINGLET OXYGEN Abstract— NHIK 3025 cells were incubated with Photofrin II (PII) and/or tetra (3‐hydroxyphenyl)porphyrin (3THPP) and exposed to light at either 400 or 420 nm, i. e. at the wavelengths of the maxima of the fluorescence excitation spectra of the two dyes. The kinetics of the photodegradation of the dyes were studied. When present separately in the cells the two dyes are photodegraded with a similar quantum yield. 3THPP is degraded 3–6 times more efficiently by light quanta absorbed by the fluorescent fraction of 3THPP than by light quanta absorbed by the fluorescent fraction of PII present in the same cells. The distance diffused by the reactive intermediate, supposedly mainly 1 O2 , causing the photodegradation was estimated to be on the order of 0.01–0.02 μm, which corresponds to a lifetime of 0.01–0.04 μs of the intermediate in the cells. PII has binding sites at proteins in the cells as shown by an energy transfer band in the fluorescence excitation spectrum at 290 nm. During light exposure this band decays faster than the Soret band of PII under the present conditions. Photoproducts (1 O2 etc.) generated at one binding site contribute significantly in the destruction of remote binding sites.
Tập 53 Số 4 - Trang 549-553 - 1991
PHOTOPHYSICAL AND PHOTOSENSITIZING PROPERTIES OF BENZOPORPHYRIN DERIVATIVE MONOACID RING A (BPD‐MA)* Abstract The photophysical properties of benzoporphyrin derivative monoacid ring A (BPD‐MA), a second‐generation photosensitizer currently in phase II clinical trials, were investigated in homogeneous solution. Absorption, fluorescence, triplet‐state, singlet oxygen (O2 (1 Δg )) sensitization studies and photobleaching experiments are reported. The ground state of this chlorin‐type molecule shows a strong absorbance in the red (λ≈ 688 nm, ɛ≈ 33 000 M −1 cm−1 in organic solvents). For the singlet excited state the following data were determined in methanol: energy level, Es = 42.1 kcal mol−1 , lifetime, Φf = 5.2 ns and fluorescence quantum yield, Φf = 0.05 in air‐saturated solution. The triplet state of BPD‐MA has a lifetime, τf >. 25 ns, an energy level, ET = 26.9 kcal mol−1 and the molar absorption coefficient is ɛT = 26 650 M−1 cm−1 at 720 nm. A dramatic effect of oxygen on the fluorescence (φf ) and intersystem crossing (φT ) quantum yields has been observed. The BPD‐MA presents rather high triplet (φT = 0.68 under N2 ‐saturated conditions) and singlet oxygen (φΔ = 0.78) quantum yields. On the other hand, the presence of oxygen does not significantly modify the photobleaching of this photostable compound, the photodegradation quantum yield (φPb ) of which was found to be on the order of 5 × 10−5 in organic solvents.
Tập 59 Số 3 - Trang 328-335 - 1994
EPR STUDIES ON SINGLET OXYGEN PRODUCTION BY PORPHYRINS Abstract— EPR studies of the porphyrin‐sensitized photooxidation of 2, 2, 6,6‐tetramethyl‐piperidine to the nitroxide demonstrate that all the porphyrins examined are able to generate 1 O2 , although the efficiency of the photoprocess is dependent on the nature of the side chains. Incorporation of metal ions into the porphyrin molecule depresses or even inhibits the formation of 1 O2 . Comparison of these results with previously obtained kinetic data points out that the efficiency of porphyrins as photosensitizes is controlled by the lifetime of their lowest triplet state.
Tập 28 Số 2 - Trang 257-259 - 1978
THE PHOTOCHEMICAL YIELD OF SINGLET OXYGEN FROM PORPHYRINS IN DIFFERENT STATES OF AGGREGATION Abstract— Aqueous solutions of hematoporphyrin and hematoporphyrin derivatives were exposed to light. When present in such solutions tryptophan is degraded by a singlet oxygen mechanism. This is true for excitation at 396 nm, where porphyrin monomers have their absorption maximum, as well as for excitation at 360 nm, where porphyrin aggregates seem to absorb strongly. The quantum yield of singlet oxygen production is similar within 25% for excitation at 396 and 360 nm while the fluorescence quantum yield is more than a factor 2 lower for excitation at 360 nm than for excitation at 396 nm. Photoexcitation of the clinically used hematopotophyrin derivatives photofrin I and photofrin II produces singlet oxygen with significantly smaller yields than photoexcitation of hematoporphyrin. Thus, the aggregates present in solutions of photofrin I and photofrin II are of a different nature than those present in aqueous solutions of hematoporphyrin.
Tập 39 Số 4 - Trang 445-449 - 1984
STRATEGIES FOR SELECTIVE CANCER PHOTOCHEMOTHERAPY: ANTIBODY‐TARGETED and SELECTIVE CARCINOMA CELL PHOTOLYSIS* Abstract A principle objective in chemotherapy is the development of modalities capable of selectively destroying malignant cells while sparing normal tissues. One new approach to selective photochemo‐therapy, antibody‐targeted photolysis (ATPL) uses photosensitizers (PS) coupled to monoclonal antibodies (MAbs) which bind to eel) surface antigens on malignant cells. Selective destruction of human T leukemia cells (HBP‐ALL) was accomplished by coupling the efficient PS chlorin e 6 to an anti‐T cell MAb using dextran carriers. Conjugates with chlorin : MAb ratios of 30 : 1 retained > 85% MAb binding activity, and had a quantum yield for singlet oxygen production of 0.7 ±0.1, the same as that of free chlorin e 6 . Cell killing was dependent on the doses of both MAb‐PS and 630‐670 nm light, and occurred only in target cell populations which bound the MAb. On the order of 1010 singlet oxygen molecules were necessary to kill a cell.A second approach to specific photochemotherapy, selective carcinoma cell photolysis (SCCP), relies on preferential accumulation of certain cationic PS by carcinoma cell mitochondria. We have evaluated several classes of cationic dyes, and in the case of N,N′‐bis ‐(2‐ethyl‐1,3‐dioxolane)‐krypto‐cyanine (EDKC) and some of its analogs, have demonstrated highly selective killing of human squamous cell, bladder and colon carcinoma cells in vitro. In isolated mitochondria, EDKC uptake and fluorescence depended on membrane potential, and the dye specifically photosensitized damage to Complex I in the electron transport chain. N,N′‐bis ‐(2‐ethyl‐1,3‐dioxolane)‐kryptocyanine and some of its analogs accumulated within subcutaneous xenografts of human tumors in nude mice with tumor : skin ratios > 8. Photoirradiation caused significant inhibition of tumor growth, without cutaneous phototoxicity.
Tập 46 Số 1 - Trang 83-96 - 1987