THERMOLUMINESCENCE and OXYGEN EVOLUTION FROM A THERMOPHILIC BLUE-GREEN ALGA OBTAINED AFTER SINGLE-TURNOVER LIGHT FLASHES*

Abstract— Oxygen evolution and thermoluminescence (TL) studies on a thermophilic blue-green alga Synechococcus vulcanus Copeland revealed the following: (a) The deactivations of the S₃ and S₂ states of the Oxygen Evolving Complex, at room temperature, have half-times of ～200 and 75 s, respectively, instead of 30 and 20 s found in mesophilic plants, (b) The TL band(s) “B”, due to the recombination of the state S₂ or S₃ and Q_B, the reduced secondary quinone acceptor, is(are) at50–55°C instead of25–30°C; the intensity of this band oscillates with a period of 4 with maxima on the 2nd and the 6th flashes, (c) The TL band “D” in the presence of diuron, due to the recombination of S₂ and the reduced primary quinone acceptor Q_A,^? occurs at ～35°C instead of0–10°C. (d) Furthermore, the ratio of Q_B^? to Q_B in dark-adapted S. vulcanus cells is close to 1 as in intact spinach leaves, but not 0.43 as in isolated thylakoids from spinach.     

ACTION SPECTRA FOR PHOTOREACTIONS I AND II OF PHOTOSYNTHESIS IN THE BLUE-GREEN ALGA ANACYSTIS NIDULANS

Abstract— Action spectra for photoreactions I and II of photosynthesis were obtained for Anacystis nidulans and three of its variants which had altered chlorophyll/phycocyanin ratios. The spectra are properly scaled to each other. They provide information on contributions of phycocyanin and chlorophyll to initial absorption and final distribution of excitation energy to reaction centers I and II. In normally pigmented cells the light harvesting pigments for photoreaction I include about 40% of the phycocyanin and 84% of the chlorophyll. Both in normal cells and in cells with altered pigmentation excitation energy from phycocyanin is delivered to photoreaction II via a small number of chlorophylls. In response to alterations in chlorophyll/phycocyanin ratio Action I spectra showed large variations whereas Action II spectra were essentially invariant. The result is taken to mean that alteration in chlorophyll components in Anacystis is attended by a special restriction: there are only small changes in amount of chlorophyll accessible to photoreaction II in the face of large changes in amount committed to photoreaction I.     

ACTION SPECTRA FOR ULTRAVIOLET KILLING AND PHOTOREACTIVATION IN THE BLUE-GREEN ALGA AGMENELLUM QUADRUPLICATUM

Abstract— The action spectrum for photoreactivation has been determined in a coccoid blue-green alga, Agmenellum quadruplicatum. The spectrum is rather similar to that recorded for Streptomyces griseus conidia, with some suggestion of a little more structure. The action spectrum suggests possible carotenoid involvement; however, no other evidence for this could be found. The action spectrum for u.v. killing is also broad with some evidence of fine structure. The possible implication of tetrahydropteridines or c -phycocyanin as chromophores in the region 240–300 nm, along with DNA, is pointed out.     

EXCITON ANNIHILATION IN THE ISOLATED PHYCOBILIPROTEINS FROM THE BLUE-GREEN ALGA NOSTOC SP. USING PICOSECOND ABSORPTION SPECTROSCOPY

Abstract— Phycobilisomes from the blue-green alga Nostoc sp. contain the phycobiliproteins: c -phycoerythrin ( c -PE), c -phycocyanin ( c -PC) and allophycocyanin (APC). The depletion and the recovery of the ground states for the individual phycobiliproteins were measured using picosecond (ps) absorption spectroscopy. In all cases the depletion time was Glops. The recovery was found to be non-exponenzial which could be fitted to a single exponential ('fast' component) and a second component with a relaxation time of > 300ps. The recovery times of the fast component were found to be intensity dependent and for c -PE, c -PC and APC were measured to be 19, 27 and 35ps, respectively, at intensity ( I ) ∼ 7 × 10²⁰ photons/m² and increased to 54, 55 and 67 ps, respectively, at I ∼ 8 × 10¹⁹ photons/m2. The ps absorption data support the assignment of the'fast' component to singlet-singlet exciton annihilation.     

EVIDENCE FOR DARK REPAIR OF FAR ULTRAVIOLET LIGHT DAMAGE IN THE BLUE-GREEN ALGA, GLOEOCAPSA ALPICOLA

Abstract— The inactivating effect of far UV light on the unicellular blue-green alga Gloeocapsa alpicola could be totally reversed by exposure to blue light immediately after irradiation. However, if the irradiated cells were held in the dark before exposure to blue light, reversal became progressively less efficient and almost disappeared after 60–80 h holding. Caffeine and acriflavine inhibited loss of photoreversibility, suggesting an involvement of excision functions. Chloramphenicol and rifampicin slightly increased the rate of loss of photoreversibility, indicating that inducible functions play only a minor role. Split UV dose experiments indicated that light-dependent repair remained operational during dark liquid holding. These results provide preliminary evidence for dark repair in G. alpicola .     

EXCITATION ENERGY TRANSFER IN THE LIGHT HARVESTING ANTENNA SYSTEM OF THE RED ALGA Porphyridium cruentum AND THE BLUE-GREEN ALGA Anacystis nidulans: ANALYSIS OF TIME-RESOLVED FLUORESCENCE SPECTRA

Abstract— Time-resolved fluorescence spectra of intact cells of red and blue-green algae Porphyridium cruentum and Anacystis nidulans were measured by means of a ps laser and a time-correlated photon counting system. Fluorescence spectra were observed successively from various pigments in the light harvesting system in the order of phycoerythrin (PE), phycocyanin (PC), allophycocyanin (APC) and chlorophyll a (Chl a ). The spectrum changes with time in the range of0–400 ps in P. cruentum and of0–1000 ps in A. nidulans . The time-resolved spectra were analyzed into components to obtain the rise and decay curve of each fluorescence component. Overall time behaviors of the sequential fluorescence emissions from various pigments can be interpreted with a decay kinetics ofexp(–2 kt ^½). The rate constants of the energy transfer show that the energy transfer takes place much faster in the red alga P. cruentum than in the blue-green alga A. nidulans , particularly in the step PCAPC. Results also indicated that a special form of APC, far-emitting APC, exists in the pigment system of A. nidulans , but it does not mediate a main energy transfer from phycobilisome to Chl a.     

WEIGLE-REACTIVATION IN A CYANOBACTERIUM (Synechococcus PCC7934) IS INDUCED BY UV BUT NOT BY MITOMYCIN-C OR NALIDIXIC ACID

Abstract— The cyanobacterium Synechococcus PCC7943 (Anacystis nidulans 602) exhibited UV induced Weigle-reactivation of irradiated cyanophaseAs–1. Weigle-reactivation had a half-life of approximately 34 min. It was not induced by treatments with the SOS inducing agents mitomycin-C or nalidixic acid.     

COMPARATIVE ANALYSES OF ACTION SPECTRA OF GLYCOLATE EXCRETION ("PHOTORESPIRATION") AND PHOTOSYNTHESIS IN THE BLUE-GREEN ALGA AN ACYSTIS NIDULANS

Abstract. The action spectra were determined by measuring photosynthetic H¹⁴CO^-₃-fixation and ¹⁴C-glycolate excretion to the medium during 15 min exposure to light at 15 different wavelengths in the visible region using interference filters and a 2500 W high pressure Xe lamp at a constant photon flux of about 1.51 × 10¹⁹ quanta m^-2.s^-1 at all wavelengths.
When plotted on relative scales the action spectrum of glycolate excretion lies below that of photosynthesis at all wavelengths shorter than 517 nm. As glycolate excretion had an exponential relationship to photosynthetic rates, different methods were used to analyze for a specific blue light effect which demonstrated that the relative amount of glycolate excretion was depressed by blue light compared with that by green and red. The greatest difference was observed around 460–480 nm. However, on statistical grounds it is not permitted to draw a difference spectrum which might indicate the absorption characteristics of pigment(s) involved.
A hypothesis is discussed assuming that some glycolate is consumed in an oxidation process for supply of electrons to Photosystem I when Photosystem II is poorly excited in the blue region of the spectrum, which was the case for Anacystis used in the present investigation.     

THE SOLID STATE REACTIONS AND TRANSITIONS IN HIGH POLYMERIC SYSTEMS Ⅲ. THE BULK CRYSTALLIZATION OF LANTHANIDECATALYTICALLY POLYMERIZED POLYDIENES

For the mechanism of isothermal bulk crystallization of high polymers, beside the nucleation and growth steps, the unimpingement of growing crystal aggregates should be taken into account for the modification of the Avrami equation. Starting from Poisson distribution function of growing crystal aggregates, the probability of the unimpinging ones should be P(0)+P(1), then the Q-modified Avrami equation thus derived can be expressed aswhere V0 represents the volume fraction of crystal aggregates at crystallization time t at a given temperature, while the exponent n on t relates to the mode of nucleation and growth, and K_q is the corresponding shape factor. This Q-modified one is verified satisfactory by the isothermal bulk crystallization of lanthanidecatalytically polymerized polybutadiene (Ln-PB), polyisoprene (Ln-PIR) and their copolymers (LnPB/IR). Furthermore, the proposed mechanism is well identified by the change of morphological state during the course of crystallization of the corresponding east film of Ln-PB TR (92/8) at-60°(Fig. 1).Upon examination of the influence of the number of entanglement on crystallization rate, it reveals the existence of two stages of entanglementation, the primary and the secondary ones (Fig. 19)The equation for dependence of molecular weight and entanglement on bulk crystallization rate has been derived as Eq. 13 or 18 for Ln-PB, and verified by the experimental rate data of well fractionated Ln-PB samples crystallized at -9.1 to -15℃(Fig.20).     

FLUORESCENCE RELAXATION KINETICS AND QUANTUM YIELD FROM THE PHYCOBILISOMES OF THE BLUE-GREEN ALGA NOSTOC SP. MEASURED AS A FUNCTION OF SINGLE PICOSECOND PULSE INTENSITY*

Abstract— A detailed experimental study of the effect of intensity of a 6 ps excitation pulse on the decay kinetics and yield from phycobilisomes (PBsomes) is presented. The fluorescence from the c-phycoerythrin (PE) emission from PBsomes was found to decay as a single exponential with a time of 31 ± 4ps for an excitation intensity <10¹⁴ photons/cm² per pulse. The risetime of the c-phycocyanin (PC) and allophycocyanin (APC) emission from PBsomes was found to be 34 ± 13 ps. Therefore, at low excitation intensities, the energy transfer time between the constituent phycobiliproteins, PE and PC, is measured to be 34 ± 13ps from the fluorescence decay time of PE and the fluorescence risetime of the PC and APC emission. The fluorescence yield from the PE emission component in PBsomes was found to be intensity dependent for excitation intensities >10¹⁴ photons/cm². The decrease in yield with increased intensity in this case occurred at a higher intensity than in the isolated phycobiliprotein PE. The fluorescence yield of the PC and APC emission component was also found to decrease markedly with increasing excitation intensity. This is in contrast to the case of the isolated phycobiliprotein APC which showed only a slight quenching of the fluorescence. The higher quenching observed for the APC emission in the PBsome evidences the higher effective absorption of APC via energy transfer from PE to PC and APC.     

ASYMMETRIC INDUCTION IN THE SOLID STATE PHOTOCHEMISTRY OF AMMONIUM SALTS*

A general approach to using crystal chirality in asymmetric synthesis is described. An example consists of the preparation of crystalline salts of dimethyl 9-amino-9,10-ethenoanthracene-11, 12-dicarboxylate (1) with optically active sulfonic acids. Photolysis of the salts in the solid state generates a product that has chiral centers in the amine-containing portion of the molecule (di-π-methane photorearrangement). The optical activity in the photoproduct was determined by polarimetry and NMR chiral shift reagent analysis, which revealed enantiomeric excesses ranging from 30 to 68% depending on the optically active sulfonic acid employed. In contrast to the results in the crystalline state, irradiation of the salts in acetonitrile gave racemic photoproduct.     

OPTICALLY DETECTED MAGNETIC RESONANCE OF THE TRYPTOPHAN PHOSPHORESCENT STATE IN NATIVE PROTEINS*

Abstract— The phosphorescent triplet state of tryptophan has been studied by the method of optically detected magnetic resonance (ODMR) at pumped helium temperatures in zero magnetic field. Only one of the triplet sublevels is found to be significantly radiative; the other two decay radiationlessly. Although the phosphorescence and ODMR decay lifetimes are influenced by spin–lattice relaxation processes at T = 1.3°K, the lifetime of the radiative level can be estimated as approximately 2 s, whereas the lifetimes of the non–radiative levels are in excess of 10 s. Comparison of the ODMR signals and the phosphorescence spectra has been made for tryptophans in native proteins with the following results: the ODMR signals of the two types of tryptophan sites in horse liver alcohol dehydrogenase can be resolved due to a shift in the D and E values of the respective triplet states; binding of the substrate tri- N -acetylglucosamine to hen lysozyme leads to a considerable narrowing of the phosphorescence peaks and ODMR signals as well as to a shift in the E value of the triplet state.
The following tentative conclusions can be reached: the tryptophan triplet D and E values are measurably affected by the environment of the chromophore in the protein, as are the linewidths of the magnetic resonance transitions. The | E | value is reduced and the magnetic resonance linewidth is increased with increasing exposure of the tryptophan to hydroxylic solvent. Although a considerable part of the width of the magnetic resonance transition can be ascribed to a heterogeneity of environments in the sample, there appears to exist an intrinsic line–broadening process which at present is not understood.     

ROLE OF THE TRYPTOPHAN FLUORESCENT STATE IN THE ULTRAVIOLET-INDUCED INACTIVATION OF β-TRYPSIN*

Abstract— Stern-Volmer quenching constants for β-trypsin at pH 3 were determined for fluorescence quenching by histidine, acrylamide, and nitrate ion. A modified Stern-Volmer plot (Lehrer, 1971) was employed to show that all of the fluorescent tryptophanyl residues of β-trypsin were equally susceptible to quenching by acrylamide at pH 3 when the enzyme was either in its native conformation or denatured in 6 M guanidine hydrochloride (GuHCl). Fluorescence lifetime measurements indicated that acrylamide quenched β-trypsin fluorescence by a purely collisional mechanism. Solvation of tryptophanyl residues of the protein was maximal at 2.5 M GuHCl, as monitored by fluorescence emission wavelength.
Investigations of the ultraviolet-induced inactivation of β-trypsin at 295 nm were performed in the presence of acrylamide at pH 3. The quantum yields for enzyme inactivation and indole destruction (determined using the PDAB reagent) were unchanged upon depopulation of the fluorescent state by 65 per cent, whether the enzyme was in its native conformation or denatured by 6 M GuHCl. It is concluded that the fluorescent state of tryptophanyl residues of β-trypsin is not involved in enzyme inactivation or tryptophan destruction.     

PHOTOREACTIVATION and EXCISION REPAIR OF UV INDUCED PYRIMIDINE DIMERS IN THE UNICELLULAR CYANOBACTERIUM GLOEOCAPSA ALPICOLA (SYNECHOCYSTIS PCC 6308)

Abstract— The survival curve obtained after UV irradiation of the unicellular cyanobacterium Synecho-cystis is typical of a DNA repair competent organism. Inhibition of DNA replication, by incubating cells in the dark, increased resistance to the lethal effects of UV at higher fluences. Exposure of irradiated cells to near ultraviolet light(350–500 nm) restored viability to pre-irradiation levels. In order to measure DNA repair activity, techniques have been developed for the chromatographic analysis of pyrimidine dimers in Synechocystis. The specificity of this method was established using a haploid strain of Sacchar-omyces cerevisiae. In accordance with the physiological responses of irradiated cells to photoreactivating light, pyrimidine dimers were not detected after photoreactivation treatment. Incubation of irradiated cells under non-photoreactivating growth conditions for 15 h resulted in complete removal of pyrimidine dimers. It is concluded that Synechocystis contains photoreactivation and excision repair systems for the removal of pyrimidine dimers.     

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.     

CHLOROPHYLL PHOTOCHEMISTRY IN CONDENSED MEDIA—II. TRIPLET STATE QUENCHING AND ELECTRON TRANSFER TO QUINONE IN LIPOSOMES*

The fate of excitation energy and electron transfer to quinones within Chl-a-containing phosphatidyl choline liposomes has been investigated. The bilayer membrane of the liposome stabilizes the Chl triplet state, as evidenced by a three-fold increase in the lifetime over that observed in ethanol solution. The relative triplet yield follows the relative fluorescence yield, indicative of quenching at the singlet level. Triplet state lifetimes are markedly shortened as the Chl concentration is increased, demonstrating that quenching occurs at the triplet level as well. This process is shown to be due to a collisional de-excitation. In the presence of quinones, the Chl triplet reduces the quinone resulting in production of long-lived electron transfer products. The percent conversion of Chl triplet to cation radical when benzoquinone is employed as acceptor is approximately 60 ± 10%, which is slightly less than in ethanol solution (70 ± 10%). The lifetime of the radical, however, can be as much as 1900 times longer. With respect to potentially useful photochemical energy conversion, the magnitude of this increased lifetime is far more significant than is the decreased radical yield.