Spectroscopy flash-induced absorbance

Fig. 10. (A) Flash-induced absorbance changes at 387,430 and 455 nm in a sample of PS-I particles from Synechococcus sp. under a mild reducing condition (ascorbate+ DCIP) or containing ferricyanide (FeCy) (B) difference spectra constructed from the aA amplitudes at the beginning and end ofthe 200-ns phase, i.e., at 5 ns and 1.6 /iS, respectively. The spectrum in the inset of (B) represents AA [P700 A,-] - [P700 A,] measured at 10 K (taken from Fig. 4 above). The dotted-line difference spectrum in (B) is that for [P700 -P700]. Figure source Brettel (1988) Electron transfer fifom Ay to an iron-sulfur center with tw=2O0 ns at room temperature in photosystem I. Characterization by flash absorption spectroscopy. FEBS Lett239 95,96.

Fig. 17. Flash-induced absorbance changes in a PS-I monomer complex of Synechocystis 6803 at 820 nm (A) and at 480 and 580 nm (B), without and with Fd (isolated from Synechocystis). Net Fd signals at 480 and 580 nm compensated for the antenna-pigment triplet contributions are aiso shown. Figure source S6tif and Bottin (1994) Laser flash absorption spectroscopy study of ferredoxin reduction by photosystem i in Synechocystis sp. PCC 6803 Evidence for submicrosecond and microsecond kinetics. Biochemistry 33 8497.

The energy released as heat in the course of the nonradiative decay of P to the ground state and detected as a pressure wave by laser-induced optoacoustic spectroscopy (LIOAS) exhibits positive deviations (i.e., a> 1 cf. Eq. (1)) from the values which were calculated on the basis of the absorption spectrum of Pr alone (Figure 15) [90,115]. This indicates that already within the 15-ns duration of the excitation flash, one or several intermediates must have been formed. These in turn, within the same interval, may again absorb light from an intense laser flash and (at least in part) dissipate heat upon their return to the ground state of the same species (internal conversion) and/or to Pr (photochemical back reaction). The formation of primary photoproducts within the nanosecond flash duration was of course to be expected in view of the much shorter lifetimes of the photochromic fluorescence decay compo-... 

The primary acceptor in PS II is a plastoquinone, PQ, as ascertained from optical absorbance difference spectroscopy [46], Until recently, the EPR spectrum of the semiquinone escaped observation, and only the advent of preparation methods for PS II subchloroplast particles made its recording possible. As surmised earlier, the spectrum of the intact acceptor [47] very much resembled the very broad qui-none-iron acceptor complex in purple bacteria, whereas in iron-depleted PS II particles the narrow spectrum typical of an immobilized semiquinone was found [48], As in the bacterial photosystem, flash-induced reduction of Q, of the second quinone, Qb, or of both resulted in somewhat different EPR spectra, indicative of structural changes that influence the magnetic interaction between the semiquinone and the non, and/or between the two semiquinones [49],... 

Fig. 8. Kinetics of optical changes induced by 150-fs, 850-nm laser flashes (XoxJ in Rb. sphaeroides reaction centers. Changes are monitored at several wavelengths (top row) specifically absorbed by various pigment molecules ( tmon)- Solid traces are for the measured absorbance changes and the dotted lines represent the best fit corresponding to a relaxation time of 2.8-ps. Figure source Martin, Breton, Hoff, Migus and Antonetti (1986) Femtosecond spectroscopy of electron transform the reaction center of the photosynthetic bacterium Rhodopseudomonas sphaeroides R-26 Direct electron transfer from the dimeric bacteriochloro-phyllprimary donor to the bacteriopheophytin acceptor with a time constant of 2.8 0.2 ps. Proc Nat Acad Sci, USA. 83 958-960.

Fig. 6. Absorbance changes induced by 33-ps, 850-nm laser pulses in Complex 1 obtained from membranes of the green sulfur bacterium Pc. aestuarff. (A) Membrane with "closed RCs (sample containing FeCy and under background Illumination) (B) membrane with open RCs (sample containing Asc and PMS). Solid-line traces represent absorbance changes observed at the time the excitation flash was applied, and the dotted-line traces are for changes observed at 350 ps after the flash. Figure source Shuvalov, Amesz and Duysens (1986) Picosecond spectroscopy of isolated membranes of the photosynthetic green sulfur bacterium Prosthecochloris aestuarii upon selective excitation of the primary electron donor. Biochim Biophys Acta. 851 2, 3.

Fig. 5. (A) AA at 694 nm in TSF-I particles poised at 200 mV and excited by 50-ps flashes at 694.3 nm [(trace (a)] and AA measured in TSF-I particles with P700 pre-oxidized by background illumination [trace (b)] (B) AA measured in TSF-I particles poised at -625 mV (note the different scales for the time axes) (C) AA at 694 nm measured in TSF-I particles (a) poised at 200 mV, (b) P700 pre-oxidized by continuous illumination, and (c) heat treated to inactivate the bound iron-sulfur centers (D) AA (red-region) measured in TSF-I particles 150-ps and 800-ps after the flash 30-ps flashes at either 708- or 689-nm were used [see data-point code in the inset) Note the different absorbance scales used. (E) AA (450-600 nm) induced by 30-ps, 689-nm flashes (F) solid trace is the difference between AA measured at 150-ps and 800 ps the dashed trace is the in vitro difference spectrum for Chl-a anion radical, shifted toward the red by -25 nm. Figure source (A) and (B) from Shuvalov, Ke and Dolan (1979) Kinetic and spectral properties of the intermediary eiectron acceptor A, in photosystem I. Subnanosecond spectroscopy. FEBS Lett 100 6 (C)-(F) from Shuvalov, Klevanik, Sharkov, Kryukov and Ke (1979) Picosecond spectroscopy of photosystem I reaction centers. FEBS Lett 107 314, 315.

Fig. 6. (A) Picosecond pulse-induced ( ) and continuous light-induced (x) difference spectrum for [P700 -P700] in PS-1 particles poised at - 200 mV (B) Difference spectrum in pre-reduced PS-1 particle induced by 35-ps flash, recorded 500 ps after the flash, and corrected for the absorbance changes due to excited states of antenna chlorophyll (C) the difference spectrum between (B) and (A), yielding the AACAu -AJ. Figure source Nuijs, Shuvalov, van Gorkom, Plijter and Duysens (1986) Picosecond absorbance difference spectroscopy on the primary reactions and the antenna-excited states in photosystem i particles. Biochim Biophys Acta 850 316, 317.

Fig. 16. Absorbance changes measured at 480 nm and associated with ferredoxin reduction induced at 660-nm by 1-r s dye laser flashes. (A) In the absence and presence of spinach ferredoxin baseline for each trace is shifted for clarity (B) plot of rate constant vs. concentration of ferredoxins from spinach and the green alga Monoraphidium braunni. Figure source Herv s, Navarro and Toltin (1992) A laser flash spectroscopy study of the kinetics of electron transfer from spinach photosystem I to spinach and algal ferredoxins. Photochem Photobiol 56 321.

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