Stark spectroscopy of the light-harvesting complex II in different oligomerisation states

The electric field-induced absorption changes (Stark effect) of light-harvesting complex II (LHCII) in different oligomerisation states-monomeric, trimeric and aggregated-have been probed at 77 K. All the chlorophyll (Chl) a molecules exhibit electro-optic properties in the Q(y) absorption region characterized by a change in dipole moment /Deltamu-->/ =0.6+/-0.06D/f and polarizability, Tr(Deltaalpha;) approximately 55+/-5 A(3)/f(2) upon electronic excitation, which are similar to those of unbound monomeric Chl a, indicating the absence of strong delocalization of the excitations which would be expected in the presence of strong excitonic interactions. The Stark effect in the Chl b absorption region is significantly bigger with /Deltamu-->/ values of the order of 2.0+/-0.2 D/f and it is attributed to strong interactions with neoxanthin molecules. Clear oligomerisation-dependent differences are observed in the carotenoid region, mainly due to the appearance of a new xanthophyll absorption band at 509 in the spectra of trimers and oligomers. It is ascribed to some lutein molecules, in agreement with previous experimental observations. The electro-optic properties of these lutein molecules are significantly different from those of the other xanthophylls in LHCII, which do not exhibit such a big change in dipole moment upon electronic excitation (/Deltamu-->/ =14.6+/-2.0 D/f). Upon aggregation of LHCII some extra absorption appears on the red side of the main Chl a Q(y) absorption band. In contrast to an earlier suggestion [J. Phys. Chem., A 103 (1999) 2422], no indications are found for the charge-transfer character of the corresponding band. The assignments of the S(2) electronic transitions of neoxanthin and lutein in LHCII and possible origins of the Stark effect are discussed.     

Spectral substructure and excitonic interactions in the minor photosystem II antenna complex CP29 as revealed by nonlinear polarization spectroscopy in the frequency domain

CP29 (the lhcb4 gene product), a minor photosystem II antenna complex, binds six chlorophyll (Chl) a, two Chl b, and two to three xanthophyll molecules. The Chl a/b Q(y) absorption band substructure of CP29 (purified from spinach) was investigated by nonlinear polarization spectroscopy in the frequency domain (NLPF) at room temperature. A set of NLPF spectra was obtained at 11 probe wavelengths. Seven probe wavelengths were located in the Q(y) spectral region (between 630 and 690 nm) and four in the Soret band (between 450 and 485 nm). Evaluation of the experimental data within the framework of global analysis leads to the following conclusions: (i) The dominant Chl a absorption (with a maximum at 674 nm) splits into (at least) three subbands (centered at 660, 670, and 681.5 nm). (ii) In the Chl b region two subbands can be identified with maxima located at 640 and 646 nm. (iii) The lowest energy Q(y) transition (peaking at 681.5 nm) is assigned to a Chl a which only weakly interacts with other Chl aor b molecules by incoherent F?rster-type excitation energy transfer. (iv) Pronounced excitonic interaction exists between certain Chl a and Chl b molecules, which most likely form a Chl a/b heterodimer. The subbands centered at 640 and 670 nm constitute a strongly coupled Chl a/b pair. The findings of the study indicate that the currently favored view of spectral heterogeneity in CP29 being due essentially to pigment-protein interactions has to be revised.     

Excitation energy transfer in the LHC-II trimer: a model based on the new 2.72 Å structure

Energy transfer of the light harvesting complex LHC-II trimer, extracted from spinach, was studied in the Q(y) region at room temperature by femtosecond transient absorption spectroscopy. Configuration interaction exciton method [Linnanto et al. (1999) J Phys Chem B 103: 8739-8750] and 2.72 A structural information reported by Liu et al. was used to calculate spectroscopic properties and excitation energy transfer rates of the complex. Site energies of the pigments and coupling constants of pigment pairs in close contact were calculated by using a quantum chemical configuration interaction method. Gaussian random variation of the diagonal and off-diagonal exciton matrix elements was used to account for inhomogeneous broadening. Rate calculations included only the excitonic states initially excited and probed in the experiments. A kinetic model was used to simulate time and wavelength dependent absorption changes after excitation on the blue side of the Q(y) transition and compared to experimentally recorded rates. Analysis of excitonic wavefunctions allowed identification of pigments initially excited and probed into later. It was shown that excitation of the blue side of the Q(y) band of a single LHC-II complex results in energy transfer from chlorophyll b's of the lumenal side to chlorophyll a's located primarly on one of the monomers of the stromal side.     

Mutant trimers of light-harvesting complex II exhibit altered pigment content and spectroscopic features

Mutants of plant light-harvesting complex II (LHC-II) were produced by refolding the complex in vitro from bacterially expressed apoprotein and purified pigments by a method which yields native-like LHC-II in a single step. Amino acid residues known from the structure of the complex [Kühlbrandt, W., et al. (1994) Nature 367, 614-621] to bind chlorophyll (Chl) were replaced with nonbinding residues by site-directed mutagenesis. Recombinant monomeric and trimeric pigment-protein complexes were separated by density gradient centrifugation, and their pigment composition was determined. Six out of nine mutants formed trimers with Chl a:Chl b ratios and Chl contents which suggested they were lacking one Chl a or b per polypeptide. In this way, the identities of Chls a1, a2, a3, b5, and b6 were confirmed as Chl a or b, respectively, whereas Chl b3 in the structure was found to be a Chl a. Absorption and fluorescence emission spectra of the mutant lacking Chl a2 indicated a central role for this Chl in energy transfer to the reaction center.     

Energy and electron transfer in photosystem II of a chlorophyll b-containing Synechocystis sp. PCC 6803 mutant

Using a Synechocystis sp. PCC 6803 mutant strain that lacks photosystem (PS) I and that synthesizes chlorophyll (Chl) b, a pigment that is not naturally present in the wild-type cyanobacterium, the functional consequences of incorporation of this pigment into the PS II core complex were investigated. Despite substitution of up to 75% of the Chl a in the PS II core complex by Chl b, the modified PS II centers remained essentially functional and were able to oxidize water and reduce Q(A), even upon selective excitation of Chl b at 460 nm. Time-resolved fluorescence decay measurements upon Chl excitation showed a significant reduction in the amplitude of the 60-70 ps component of fluorescence decay in open Chl b-containing PS II centers. This may indicate slower energy transfer from the PS II core antenna to the reaction center pigments or slower energy trapping. Chl b and pheophytin b were present in isolated PS II reaction centers. Pheophytin b can be reversibly photoreduced, as evidenced from the absorption bleaching at approximately 440 and 650 nm upon illumination in the presence of dithionite. Upon excitation at 685 nm, transient absorption measurements using PS II particles showed some bleaching at 650 nm together with a major decrease in absorption around 678 nm. The 650 nm bleaching that developed within approximately 10 ps after the flash and then remained virtually unchanged for up to 1 ns was attributed to formation of reduced pheophytin b and oxidized Chl b in some PS II reaction centers. Chl b-containing PS II had a lower rate of charge recombination of Q(A)(-) with the donor side and a significantly decreased yield of delayed luminescence in the presence of DCMU. Taken together, the data suggest that Chl b and pheophytin b participate in electron-transfer reactions in PS II reaction centers of Chl b-containing mutant of Synechocystis without significant impairment of PS II function.     

Peridinin-chlorophyll-protein reconstituted with chlorophyll mixtures: preparation, bulk and single molecule spectroscopy

Reconstitution of the 16 kDa N-terminal domain of the peridinin-chlorophyll-protein, N-PCP, with mixtures of chlorophyll a (Chl a) and Chl b, resulted in 32 kDa complexes containing two pigment clusters, each bound to one N-PCP. Besides homo-chlorophyllous complexes, hetero-chlorophyllous ones were obtained that contain Chl a in one pigment cluster, and Chl b in the other. Binding of Chl b is stronger than that of the native pigment, Chl a. Energy transfer from Chl b to Chl a is efficient, but there are only weak interactions between the two pigments. Individual homo- and hetero-chlorophyllous complexes were investigated by single molecule spectroscopy using excitation into the peridinin absorption band and scanning of the Chl fluorescence, the latter show frequently well resolved emissions of the two pigments.     

Carotenoid-to-chlorophyll energy transfer in recombinant major light-harvesting complex (LHCII) of higher plants. I. Femtosecond transient absorption measurements

The energy transfer kinetics from carotenoids to chlorophylls and among chlorophylls has been measured by femtosecond transient absorption kinetics in a monomeric unit of the major light-harvesting complex (LHCII) from higher plants. The samples were reconstituted complexes with different carotenoid contents. The kinetics was measured both in the carotenoid absorption region and in the chlorophyll Q(y) region using two different excitation wavelengths suitable for selective excitation of the carotenoids. Analysis of the data shows that the overwhelming part of the energy transfer from the carotenoids occurs directly from the initially excited S(2) state of the carotenoids. Only a small part (<20%) may possibly take an S(1) pathway. All the S(2) energy transfer from carotenoids to chlorophylls occurs with time constants <100 fs. We have been able to differentiate among the three carotenoids, two luteins and neoxanthin, which have transfer times of approximately 50 and 75 fs for the two luteins, and approximately 90 fs for neoxanthin. About 50% of the energy absorbed by carotenoids is initially transferred directly to chlorophyll b (Chl b), while the rest is transferred to Chl a. Neoxanthin almost exclusively transfers to Chl b. Due to various complex effects discussed in the paper, such as a specific coupling of Chl b and Chl a excited states, the percentage of direct Chl b transfer thus is somewhat lower than estimated by us previously for LHCII from Arabidopsis thaliana. (Connelly, J. P., M. G. Müller, R. Bassi, R. Croce, and A. R. Holzwarth. 1997. Biochemistry. 36:281). We can distinguish three different Chls b receiving energy directly from carotenoids. We propose as a new mechanism that the carotenoid-to-Chl b transfer occurs to a large part via the B(x) state of Chl b and to the Q(x) state, while the transfer to Chl a occurs only via the Q(x) state. We find no compelling evidence in favor of a substantial S(1) transfer path of the carotenoids, although some transfer via the S(1) state of neoxanthin can not be entirely excluded. The S(1) lifetimes of the two luteins were determined to be 15 ps and 3.9 ps. A detailed quantitative analysis and kinetic model of the processes described here will be presented in a separate paper.     

Analysis of absorption spectra of purple bacterial reaction centers in the near infrared region by higher order derivative spectroscopy

Reaction centers (RCs) of purple bacteria are uniquely suited objects to study the mechanisms of the photosynthetic conversion of light energy into chemical energy. A recently introduced method of higher order derivative spectroscopy [I.K. Mikhailyuk, H. Lokstein, A.P. Razjivin, A method of spectral subband decomposition by simultaneous fitting the initial spectrum and a set of its derivatives, J. Biochem. Biophys. Methods 63 (2005) 10-23] was used to analyze the NIR absorption spectra of RC preparations from Rhodobacter (R.) sphaeroides strain 2R and Blastochloris (B.) viridis strain KH, containing bacteriochlorophyll (BChl) a and b, respectively. Q(y) bands of individual RC porphyrin components (BChls and bacteriopheophytins, BPheo) were identified. The results indicate that the upper exciton level P(y+) of the photo-active BChl dimer in RCs of R. sphaeroides has an absorption maximum of 810nm. The blue shift of a complex integral band at approximately 800nm upon oxidation of the RC is caused primarily by bleaching of P(y+), rather than by an electrochromic shift of the absorption band(s) of the monomeric BChls. Likewise, the disappearance of a band peaking at 842nm upon oxidation of RCs from B. viridis indicates that this band has to be assigned to P(y+). A blue shift of an absorption band at approximately 830nm upon oxidation of RCs of B. viridis is also essentially caused by the disappearance of P(y+), rather than by an electrochromic shift of the absorption bands of monomeric BChls. Absorption maxima of the monomeric BChls, B(B) and B(A) are at 802 and 797nm, respectively, in RCs of R. sphaeroides at room temperature. BPheo co-factors H(B) and H(A) peak at 748 and 758nm, respectively, at room temperature. For B. viridis RCs the spectral positions of H(B) and H(A) were found to be 796 and 816nm, respectively, at room temperature.     

Single molecule spectroscopy on the light-harvesting complex II of higher plants.

Spectroscopic and polarization properties of single light-harvesting complexes of higher plants (LHC-II) were studied at both room temperature and T < 5 K. Monomeric complexes emit roughly linearly polarized fluorescence light thus indicating the existence of only one emitting state. Most probably this observation is explained by efficient triplet quenching restricted to one chlorophyll a (Chl a) molecule or by rather irreversible energy transfer within the pool of Chl a molecules. LHC-II complexes in the trimeric (native) arrangement bleach in a number of steps, suggesting localization of excitations within the monomeric subunits. Interpretation of the fluorescence polarization properties of trimers requires the assumption of transition dipole moments tilted out of the symmetry plane of the complex. Low-temperature fluorescence emission of trimers is characterized by several narrow spectral lines. Even at lowest excitation intensities, we observed considerable spectral diffusion most probably due to low temperature protein dynamics. These results also indicate weak interaction between Chls belonging to different monomeric subunits within the trimer thus leading to a localization of excitations within the monomer. The experimental results demonstrate the feasibility of polarization sensitive studies on single LHC-II complexes and suggest an application for determination of the Chl transition-dipole moment orientations, a key issue in understanding the structure-function relationships.     

Primary light-energy conversion in tetrameric chlorophyll structure of photosystem II and bacterial reaction centers: II. Femto- and picosecond charge separation in PSII D1/D2/Cyt b559 complex

In Part I of the article, a review of recent data on electron-transfer reactions in photosystem II (PSII) and bacterial reaction center (RC) has been presented. In Part II, transient absorption difference spectroscopy with 20-fs resolution was applied to study the primary charge separation in PSII RC (DI/DII/Cyt b 559 complex) excited at 700 nm at 278 K. It was shown that the initial electron-transfer reaction occurs within 0.9 ps with the formation of the charge-separated state P680(+)Chl(D1)(-), which relaxed within 14 ps as indicated by reversible bleaching of 670-nm band that was tentatively assigned to the Chl(D1) absorption. The subsequent electron transfer from Chl(D1)(-) within 14 ps was accompanied by a development of the radical anion band of Pheo(D1) at 445 nm, attributable to the formation of the secondary radical pair P680(+)Pheo(D1)(-). The key point of this model is that the most blue Q(y) transition of Chl(D1) in RC is allowing an effective stabilization of separated charges. Although an alternative mechanism of charge separation with Chl(D1)* as a primary electron donor and Pheo(D1) as a primary acceptor can not be ruled out, it is less consistent with the kinetics and spectra of absorbance changes induced in the PSII RC preparation by femtosecond excitation at 700 nm.     

Spectroscopic properties of the main-form and high-salt peridinin-chlorophyll a proteins from Amphidinium carterae

The main-form (MFPCP) and high-salt (HSPCP) peridinin-chlorophyll a proteins from the dinoflagellate Amphidinium carterae were investigated using absorption, fluorescence, fluorescence excitation, two-photon, and fast-transient optical spectroscopy. Pigment analysis has demonstrated previously that MFPCP contains eight peridinins and two chlorophyll (Chl) a molecules, whereas HSPCP has six peridinins and two Chl a molecules [Sharples, F. P., et al. (1996) Biochim. Biophys. Acta 1276, 117-123]. Absorption spectra of the complexes were recorded at 10 K and analyzed in the 400-600 nm region by summing the individual 10 K spectra of Chl a and peridinin recorded in 2-MTHF. The absorption spectral profiles of the complexes in the Q(y) region between 650 and 700 nm were fit using Gaussian functions. The absorption and fluorescence spectra from both complexes exhibit several distinguishing features that become evident only at cryogenic temperatures. In particular, at low temperatures the Q(y) transitions of the Chls bound in the HSPCP complex are split into two well-resolved bands. Fluorescence excitation spectroscopy has revealed that the peridinin-to-Chl a energy transfer efficiency is high (>95%). Transient absorption spectroscopy has been used to measure the rate of energy transfer between the two bound Chls which is a factor of 2.9 slower in HSPCP than in MFPCP. The kinetic data are interpreted in terms of the F?rster mechanism describing energy transfer between weakly coupled, spatially fixed, donor-acceptor Chl a molecules. The study provides insight into the molecular factors that control energy transfer in this class of light-harvesting pigment-protein complexes.     

Organization and Stability of Polypeptides Associated with the Chlorophyll a-b Light-Harvesting Complex of Photosystem-II

In the oxygen-evolving photosystem-II (PSII) of higher plantchioroplasts and green algae, most of the light-harvesting functionis performed by the chlorophyll (Chl) a-b-protein complex (LHC-II).On the average, the LHC-II contains about 210 Chl (a+b) moleculesper PSII reaction center. The polypeptide composition, copynumber and organization of assembly in the LHC-II complex arenot fully understood at present. This work utilized the chlorinaf2 mutant of barley (lacking Chl b and having a LHC-II antennaof only 13 Chl a molecules) to determine the organization andstability of assembly of proteins in the LHC-II. High-resolutionSDS-PAGE and immunoblot analysis showed the presence of fourmain constitutive polypeptides in the wild-type LHC-II (termedhere subunits a, b, c and d) with molecular masses in the range30–25 kDa. Of those, only subunit d (a 25 kDa polypeptide)was found to occur at an equal copy number per PSII reactioncenter in both wild-type and in the Chl b-less chlorina f2 mutant.All other subunits were either absent or existed in much loweramounts in the mutant. Subunit d is a polypeptide constituentof the major Chl-protein subcomplex (CPII) of the LHC-II. Itis stably incorporated in the thylakoid membrane in the absenceof Chl b and probably binds the 13 Chl a molecules in the residualLHC-II antenna of the chlorina f2 mutant. We propose that, ofall LHC-II polypeptides, subunit d is most proximal to the PSIIcore and may serve as a linker in the process of excitationenergy transfer from the bulk LHC-II to the PSII reaction centerin chloroplasts. (Received February 25, 1992; Accepted May 12, 1992)     

Chloroplast Response in Dunaliella salina to Irradiance Stress (Effect on Thylakoid Membrane Protein Assembly and Function)

The chloroplast response in the green alga Dunaliella salina to irradiance stress was investigated. Cells were grown under low light (LL) at 100 [mu]mol photons m-2 s-1 or high light (HL) at 2000 [mu]mol photons m-2 s-1 incident intensity. LL-grown cells had a low chlorophyll (Chl) a/b ratio, an abundance of light-harvesting complex II proteins (LHC-II), and a large Chl antenna size. HL-grown cells had a higher Chl a/b ratio, relatively fewer LHC-II, and a small Chl antenna size. The more abundant higher molecular mass subunits of the LHC-II (approximately 31 kD) were selectively depleted from the thylakoid membrane of HL-grown cells. Light-shift experiments defined the kinetics of change in the subunit composition of the LHC-II and suggested distinct mechanisms in the acclimation of thylakoids to HL or LL conditions. The results showed that irradiance exerts a differential regulation on the expression of various Lhcb genes. The specific polyclonal antibodies used in this work, raised against the purified LHC-II, cross-reacted with a polypeptide of approximately 20 kD in HL-grown samples. In this work we examined the dynamics of induction of this novel protein and discuss its function in terms of a chloroplast response to the level of irradiance.     

Chlorophyll-protein composition of the thylakoid membrane from Prochlorothrix hollandica, a prokaryote containing chlorophyll b

The chlorophyll-protein complexes of the thylakoid membrane from Prochlorothrix hollandica were identified following electrophoresis under nondenaturing conditions. Five complexes, CP1-CP5, were resolved and these green bands were analyzed by spectroscopic and immunological methods. CP1 contains the photosystem I (PSI) reaction center, as this complex quenched fluorescence at room temperature, and had a 77 K fluorescence emission peak at 717 nm. CP4 contains the major chlorophyll-a-binding proteins of the photosystem II (PSII) core, because this complex contained polypeptides which cross-reacted to antibodies raised against Chlamydomonas PSII proteins 5 and 6. Furthermore, fluorescence excitation studies at 77 K indicated that only a Chl a is bound to CP4. Complexes CP2, CP3 and CP5 contained functionally bound Chl a and b as judged by absorption spectroscopy at 20 degrees C and fluorescence excitation spectra at 77 K. CP2, CP3 and CP5 all contain polypeptides of 30-33 kDa which are immunologically distinct from the LHC-II complex of higher plant thylakoids.     

Circular dichroism and magnetic circular dichroism spectra of chlorophylls a and b in nematic liquid crystals. II. Magnetic circular dichroism spectra

Absorption and magnetic circular dichroism (MCD) spectra are reported for chlorophyll (Chl) a and Chl b dissolved in nematic liquid crystal solvents. The spectra were measured with the dye molecules oriented uniaxially along the direction of. the magnetic field and measuring light beam. It is significant that under such conditions the MCD spectra recorded in the wavelength region of the Q and Soret bands of the chlorophyll are essentially unchanged with respect to rotation of the sample cell around this axis, even though there is almost complete orientation of the chlorophyll molecules by the liquid crystals. The MCD spectra of Chl a and b in the nematic liquid crystal solvents used in this study are surprisingly similar to the spectra obtained under isotropic conditions. These results illustrate an important technique with which to examine the optical spectra of dyes oriented in liquid crystal matrices in which the anisotropic effects can be reduced the negligible proportions by the application of a strong magnetic field parallel to the direction of the measuring light beam. The first deconvolution calculations are reported that describe the deconvolution of pairs of absorption and MCD spectra, in the Q and B band regions, for both Chl a and b. The spectral analysis to obtain quantitative estimates of transition energies was accomplished by carrying out detailed deconvolution calculations in which the both the absorption and MCD spectral envelopes were fitted with the same number of components; each pair of components had the same hand centres and bandwidth values. This procedure resulted in an assignment of each of the main transitions in the absorption spectra of both Chl a and b. Chl a is clearly monomeric, with Qy, Qx, By and Bx located at 671, 582, 439 and 431 nm, respectively. Analysis of the spectral data for Chl b located Qy, By and Bx, at 662, 476 and 464 nm, respectively.     

2-D gel densitometer for high-contrast and selective imaging of chlorophyll-containing protein complexes separated by non-denaturing polyacrylamide gel electrophoresis

In this work, we present a home-made two-dimensional (2-D) CCD imaging system for the monochromatic densitometry of plane gels and its application to the imaging and densitometry of chlorophyll (Chl)-containing proteins separated by non-denaturing polyacrylamide gel electrophoresis. The monochromatic imaging of separated green bands at the wavelengths corresponding to their absorption band increases their contrast. This allows a better visualization of the faint-green bands in the gel and using of samples with lower Chl content for the electrophoresis. By the comparison of 2-D densitograms of the same gel illuminated with 670 and 650 nm lights, that is, at the red absorption maximum of Chl a and b, respectively, we achieved a selective imaging of the complexes with different Chl a/b ratio. This approach was used to specify an unknown band that appeared in the gel of the sample prepared from the thylakoid membranes of preheated barley leaves.     

Low-temperature energy transfer in LHC-II trimers from the Chl a/b light-harvesting antenna of photosystem II.

Temperature dependence in electronic energy transfer steps within light-harvesting antenna trimers from photosystem II was investigated by studying Chl a pump-probe anisotropy decays at several wavelengths from 675 to 682 nm. The anisotropy lifetime is markedly sensitive to temperature at the longest wavelengths (680-682 nm), increasing by factors of 5 to 6 as the trimers are cooled from room temperature to 13 K. The temperature dependence is muted at 677 and 675 nm. This behavior is modeled using simulations of temperature-broadened Chl a absorption and fluorescence spectra in spectral overlap calculations of Förster energy transfer rates. In this model, the 680 nm anisotropy decays are dominated by uphill energy transfers from 680 nm Chl a pigments at the red edge of the LHC-II spectrum; the 675 nm anisotropy decays reflect a statistical average of uphill and downhill energy transfers from 676-nm pigments. The measured temperature dependence is consistent with essentially uncorrelated inhomogeneous broadening of donor and acceptor Chl a pigments.     

Site-directed mutations at D1-Thr179 of photosystem II in Synechocystis sp. PCC 6803 modify the spectroscopic properties of the accessory chlorophyll in the D1-branch of the reaction center

D1-Thr179, which overlies the reaction center chlorophyll Chl D1 of Photosystem II was replaced with His and Glu through site-directed mutation in Synechocystis sp. PCC 6803. Spectroscopic characterization of the mutants indicates that, compared to wild type, the main bleaching in the triplet-minus-singlet absorbance difference spectrum and the electrochromic band shift in the (P680 (+)Q A (-)-P680Q A) absorbance difference spectrum are displaced to the red by approximately 2 nm in the D1-Thr179His mutant and to the blue by approximately 1 nm in the D1-Thr179Glu mutant. These difference spectra are compared with the absorbance difference spectra, measured on the same states in the D1-His198Gln mutant in which the axial ligand D1-His198 of the special pair chlorophyll, P D1, was replaced by glutamine. Together, these results give direct evidence that (a) the reaction center triplet state, produced upon charge recombination from (3)[P (+)Pheo (-)], is primarily localized on Chl D1; (b) the cation of the oxidized donor P (+) is predominantly localized on chlorophyll P D1 of the special pair; and (c) the Q Y band of the accessory chlorophyll Chl D1 is electrochromically shifted in response to charges on P (+) and Q A (-). Light-induced absorbance difference spectra (between 650 and 710 nm), associated with the oxidation of secondary donors and the reduction of Q A, exhibit a bleaching attributed to the oxidation of a Chl Z and strong electrochromic band shifts. On the basis of mutation-induced spectroscopic changes and of structure-based calculations, we conclude that the experimental spectra are best explained by a blue-shift of the Q Y band of the accessory chlorophyll Chl D1, arising from charges on Car D2 (+) and Chl ZD2 (+) and on reduced Q A.     

Testosterone inhibits tumor necrosis factor-alpha-induced vascular cell adhesion molecule-1 expression in human aortic endothelial cells

It was shown that an increase in the bacteriochlorophyll (BChl) c antenna size observed upon lowering growth light intensities led to enhancement of the hyperchromism of the BChl c Q(y) absorption band of the green photosynthetic bacterium Chloroflexus aurantiacus. With femtosecond difference absorption spectroscopy, it was shown that the amplitude of bleaching of the oligomeric BChl c Q(y) band (as compared to that for monomeric BChl a) increased with increasing BChl c content in chlorosomes. This BChl c bleaching amplitude was about doubled as the chlorosomal antenna size was about trebled. Both sets of findings clearly show that a unit BChl c aggregate in the chlorosomal antenna is variable in size and governed by the grow light intensity, thus ensuring the high efficiency of energy transfer within the BChl c antenna regardless of its size.     

State 1/State 2 changes in higher plants and algae

Current ideas regarding the molecular basis of State 1/State 2 transitions in higher plants and green algae are mainly centered around the view that excitation energy distribution is controlled by phosphorylation of the light-harvesting complex of photosystem II (LHC-II). The evidence supporting this view is examined and the relationship of the transitions occurring in these systems to the corresponding transitions seen in red and blue-green algae is explored.Abbreviations CCCP carbonylcyanide-m-chlorophenylhydrazone - Chl a chlorophyll a - Chl b chlorophyll b - DAD diaminodurene - DBMIB 2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone - DCCD N,N-dicyclohexyl carbodiimide - DCMU 3-(3,4-dichlorophenyl)-l,l-dimethylurea (also called diuron) - FCCP carbonylcyanide-p-trifluoromethoxyphenylhydrazone - FSBA 5-fluorosulphonylbenzoyl adenosine - kDa kilodalton - LHC-II light-harvesting Chl a/Chl b protein - PMS phenazine methosulfate - PS I photosystem I - PS II photosystem II - SDS sodium dodecyl sulfate - TPTC triphenyl tin chloride This paper follows our new instructions for citation of references—authors are requested to follow Photosynth Res 10: 519–526 (1986)—editors.