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At least 19 recordsLinked to original sources

PubMed2001

Active oxygen produced during selective excitation of photosystem I is damaging not only to photosystem I, but also to photosystem II.

With the aim to specifically study the molecular mechanisms behind photoinhibition of photosystem I, stacked spinach (Spinacia oleracea) thylakoids were irradiated at 4 degrees C with far-red light (>715 nm) exciting photosystem I, but not photosystem II. Selective excitation of photosystem I by far-red light for 130 min resulted in a 40% inactivation of photosystem I. It is surprising that this treatment also caused up to 90% damage to photosystem II. This suggests that active oxygen produced at the reducing side of photosystem I is highly damaging to photosystem II. Only a small pool of the D1-protein was degraded. However, most of the D1-protein was modified to a slightly higher molecular mass, indicative of a damage-induced conformational change. The far-red illumination was also performed using destacked and randomized thylakoids in which the distance between the photosystems is shorter. Upon 130 min of illumination, photosystem I showed an approximate 40% inactivation as in stacked thylakoids. In contrast, photosystem II only showed 40% inactivation in destacked and randomized thylakoids, less than one-half of the inactivation observed using stacked thylakoids. In accordance with this, photosystem II, but not photosystem I is more protected from photoinhibition in destacked thylakoids. Addition of active oxygen scavengers during the far-red photosystem I illumination demonstrated superoxide to be a major cause of damage to photosystem I, whereas photosystem II was damaged mainly by superoxide and hydrogen peroxide.

Cell Fractionation↗

PubMed1975

Excitation spectra for photosystem I and photosystem II in chloroplasts and the spectral characteristics of the distributions of quanta between the two photosystems.

The parameters listed in the title were determined within the context of a model for the photochemical apparatus of photosynthesis. The fluorescence of variable yield at 750 nm at -196 degrees C is due to energy transfer from Photosystem II to Photosystem I. Fluorescence excitation spectra were measured at -196 degrees C at the minimum, FO, level and the maximum, FM, level of the emission at 750 nm. The difference spectrum, FM-FO, which represents the excitation spectrum for FV is presented as a pure Photosystem II excitation spectrum. This spectrum shows a maximum at 677 nm, attributable to the antenna chlorophyll a of Photosystem II units, with a shoulder at 670 nm and a smaller maximum at 650 nm, presumably due to chlorophyll a and chlorophyll b of the light-harvesting chlorophyll complex. Fluoresence at the FO level at 750 nm can be considered in two parts; one part due to the fraction of absorbed quanta, alpha, which excites Photosystem I more-or-less directly and another part due to energy transfer from Photosystem II to Photosystem I. The latter contribution can be estimated from the ratio of FO/FV measured at 692 nm and the extent of FV at 750 nm. According to this procedure the excitation spectrum of Photosystem I at -196 degrees C was determined by subtracting 1/3 of the excitation spectrum of FV at 750 nm from the excitation spectrum of FO at 750 nm. The spectrum shows a relatively sharp maximum at 681 nm due to the antenna chlorophyll a of Photosystem I units with probably some energy transfer from the light-harvesting chlorophyll complex. The wavelength dependence of alpha was determined from fluorescence measurements at 692 and 750 nm at -196 degrees C. Alpha is constant to within a few percent from 400 to 680 nm, the maximum deviation being at 515 nm where alpha shows a broad maximum increasing from 0.30 to 0.34. At wavelengths between 680 and 700 nm, alpha increases to unity as Photosystem I becomes the dominant absorber in the photochemical apparatus.

Chloroplasts↗

PubMed1996

Interaction of the 33 kDa extrinsic protein with photosystem II: rebinding of the 33 kDa extrinsic protein to photosystem II membranes which contain four, two, or zero manganese per photosystem II reaction center.

The 33 kDa extrinsic protein of photosystem II acts to enhance oxygen evolution and to stabilize the manganese cluster at low chloride concentrations. Due to controversies concerning the stoichiometry of this protein [Miyao, M., & Murata, N. (1989) Biochim. Biophys. Acta 977, 315-321, versus Xu, Q., & Bricker, T. M. (1992) J. Biol. Chem. 267. 25816-25821] we have examined the rebinding of this protein to PS II membrane preparations which contain four, two, or zero manganese per photosystem II reaction center. After rebinding, immunoquantification of the 33 kDa extrinsic protein demonstrated that each of these photosystem II membrane preparations strongly bound two copies of the 33 kDa extrinsic protein per photosystem II reaction center. The first and second stoichiometric binding constants (Ka1 and Ka2) for the binding of the 33 kDa protein to PS II centers containing four manganese were 0.42 and 0.67 nM(-1), respectively. Disruption of the manganese cluster either by removal of the chloride-sensitive manganese or extraction of the manganese cluster by alkaline Tris led to a 5-6-fold decrease in Ka1 and about a 3-fold decrease in Ka2. In all cases the binding of the two copies of the 33 kDa extrinsic protein exhibited positive cooperativity with Hill coefficients ranging from 1.6 to 2.2. These findings demonstrate that damage to the manganese cluster alters the binding affinity of the 33 kDa extrinsic protein to photosystem II but does not alter the molecularity of the binding reaction.

Binding Sites↗

PubMed1983

Electron acceptance at photosystem II in an oxygen-evolving photosystem II preparation: clear discrimination of two sites of electron acceptance for quinones and quinonediimines associated with a photosystem II preparation.

Oxygen-producing electron transport reactions of a photosystem II preparation are described. The preparation has six major peptides with apparent molecular weights of 36,000, 31,000, 28,000, 27,000, 25,000, and 21,000. Sucrose density gradient centrifugation indicates that the preparation is more homogeneous and more dense than control thylakoid membranes. The preparation photoreduces a number of known photosystem II oxidants including the Class I acceptor, ferricyanide; the Class II acceptor, 2,6-dichloroindophenol; and the Class III acceptor, 2,6-dichlorobenzoquinone. However, quinonediimines such as phenylenediimine are not reduced, suggesting that these substances are reduced at sites in the thylakoid membrane which are not found in the photosystem II preparation. All the oxygen-producing reactions are sensitive to inhibition by 3-(3,4-dichlorophenyl)-1,1-dimethylurea.

Binding Sites↗

PubMed1975

Energy transfer between photosystem II and photosystem I in chloroplasts.

A model for the photochemical apparatus of photosynthesis is presented which accounts for the fluorescence properties of Photosystem II and Photosystem I as well as energy transfer between the two photosystems. The model was tested by measuring at - 196 degrees C fluorescence induction curves at 690 and 730 nm in the absence and presence of 5mMMgCl2 which presumably changes the distrubution of excitation energy between the two photosystems. The equations describing the fluorescence properties involve terms for the distribution of absorbed quanta, alpha, being the fraction distributed to Photosystem I, and beta, the fraction to Photosystem II to Photosystem I, KT(II yields I). The data, analyzed within the context of the model, permit a direct comparison of alpha and kt(II yields I) in the absence (minus) and presence (+) of Mg-2+ :alpha minus/alpha-+ equals 1.2 and k-minus t)II yields I)/K-+T(II yields I) equal to 1.9. If the criterion that alpha + beta equal to 1 is applied absolute values can be calculated: in the presence of Mg-2+, alpha-+ equal to 0.27 and the yield of energy transfer, phi-+ t(II yields I) varied the presence of Mg-2+, alpha-+ equal to 0.27 and the yield of energy transfer, phi-+ t(II yields I) varied from 0.065 when the Photosystem II reaction centers were all open to 0.23 when they were closed. In the absence of Mg-2+, alpha-minus equal to 0.32 and phi t(II yields I) varied from 0.12 to 0.28. The data were also analyzed assuming that two types of energy transfer could be distinguished; a transfer from the light-harvesting chlorophyll of Photosystem II to Photosystem I, kt(II yields I), and a transfer from the reaction centers of Photosystem II to Photosystem I, kt(II yields I). In that case alpha-minus/alpha+ equal to 1.3, k-minus t(II yields I)/k+ t(II yields I)equal to 1.3 and k-minus t(II yields I) equal to 3.0. It was concluded, however, that both of these types of energy transfer are different manifestations of a single energy transfer process.

Chloroplasts↗

PubMed1991

Polypeptide composition of the Photosystem I complex and the Photosystem I core protein from Synechococcus sp. PCC 6301.

The polypeptide composition of the Photosystem I complex from Synechococcus sp. PCC 6301 was determined by sodium-dodecyl sulfate polyacrylamide gel electrophoresis and N-terminal amino acid sequencing. The PsaA, PsaB, PsaC, PsaD, PsaE, PsaF, PsaK and PsaL proteins, as well as three polypeptides with apparent masses less than 8 kDa and small amounts of the 12.6 kDa GlnB (PII) protein, wee present in the Photosystem I complex. No proteins homologous to the PsaG and PsaH subunits of eukaryotic Photosystem I complexes were detected. When the Photosystem I complex was treated with 6.8 M urea and ultrafiltered using a 100 kDa cutoff membrane, the resulting Photosystem I core protein was found to be depleted of the PsaC, PsaD and PsaE proteins. The filtrate contained the missing proteins, along with five proteolytically-cleaved polypeptides with apparent masses of less than 16 kDa and with N-termini identical to that of the PsaD protein. The PsaF and PsaL proteins, along with the three less than 8 kDa polypeptides, were not released from the Photosystem I complex to any significant extent, but low-abundance polypeptides with N-termini identical to those of PsaF and PsaL were found in the filtrate with apparent masses slightly smaller than those found in the native Photosystem I complex. When the filtrate was incubated with FeCl3, Na2S and beta-mercaptoethanol in the presence of the isolated Photosystem I core protein, the PsaC, PsaD and PsaE proteins were rebound to reconstitute a Photosystem I complex functional in light-induced electron flow from P700 to FA/FB. In the absence of the iron-sulfur reconstitution agents, there was little rebinding of the PsaC, psaD or PsaE proteins to the Photosystem I core protein. No binding of the truncated PsaD polypeptides occurred, either in the presence or absence of the iron-sulfur reagents. The reconstitution of the FA/FB iron-sulfur clusters thus appears to be a necessary precondition for rebinding of the PsaC, psaD and psaE proteins to the Photosystem I core protein.

Amino Acid Sequence↗

PubMed2006

Biochemical and structural analyses of a higher plant photosystem II supercomplex of a photosystem I-less mutant of barley. Consequences of a chronic over-reduction of the plastoquinone pool.

Photosystem II of higher plants is a multisubunit transmembrane complex composed of a core moiety and an extensive peripheral antenna system. The number of antenna polypeptides per core complex is modulated following environmental conditions in order to optimize photosynthetic performance. In this study, we used a barley (Hordeum vulgare) mutant, viridis zb63, which lacks photosystem I, to mimic extreme and chronic overexcitation of photosystem II. The mutation was shown to reduce the photosystem II antenna to a minimal size of about 100 chlorophylls per photosystem II reaction centre, which was not further reducible. The minimal photosystem II unit was analysed by biochemical methods and by electron microscopy, and found to consist of a dimeric photosystem II reaction centre core surrounded by monomeric Lhcb4 (chlorophyll protein 29), Lhcb5 (chlorophyll protein 26) and trimeric light-harvesting complex II antenna proteins. This minimal photosystem II unit forms arrays in vivo, possibly to increase the efficiency of energy distribution and provide photoprotection. In wild-type plants, an additional antenna protein, chlorophyll protein 24 (Lhcb6), which is not expressed in viridis zb63, is proposed to associate to this minimal unit and stabilize larger antenna systems when needed. The analysis of the mutant also revealed the presence of two distinct signalling pathways activated by excess light absorbed by photosystem II: one, dependent on the redox state of the electron transport chain, is involved in the regulation of antenna size, and the second, more directly linked to the level of photoinhibitory stress perceived by the cell, participates in regulating carotenoid biosynthesis.

Cryoelectron Microscopy↗

PubMed1997

Isolation and biochemical characterisation of monomeric and dimeric photosystem II complexes from spinach and their relevance to the organisation of photosystem II in vivo.

Membranes enriched in photosystem II were isolated from spinach and further solubilised using n-octyl beta-D-glucopyranoside (OctGlc) and n-dodecyl beta-D-maltoside (DodGlc2). The OctGlc preparation had high rates of oxygen evolution and when subjected to size-exclusion HPLC and sucrose density gradient centrifugation, in the presence of DodGlc2, separated into dimeric (430 kDa), monomeric (236 kDa) photosystem II cores and a fraction containing photosystem II light-harvesting complex (Lhcb) proteins. The dimeric core fraction was more stable, contained higher levels of chlorophyll, beta-carotene and plastoquinone per photosystem II reaction centre and had a higher oxygen-evolving activity than the monomeric cores. Their subunit composition was similar (CP43, CP47, D1, D2, cytochrome b 559 and several lower-molecular-mass components) except that the level of 33-kDa extrinsic protein was lower in the monomeric fraction. Direct solubilisation of photosystem-II-enriched membranes with DodGlc2, followed by sucrose density gradient centrifugation, yielded a super complex (700 kDa) containing the dimeric form of the photosystem II core and Lhcb proteins: Lhcb1, Lhcb2, Lhcb4 (CP29), and Lhcb5 (CP26). Like the dimeric and monomeric photosystem II core complexes, the photosystem II-LHCII complex had lost the 23-kDa and 17-kDa extrinsic proteins, but maintained the 33-kDa protein and the ability to evolve oxygen. It is suggested, with a proposed model, that the isolated photosystem II-LHCII super complex represents an in vivo organisation that can sometimes form a lattice in granal membranes of the type detected by freeze-etch electron microscopy [Seibert, M., DeWit, M. & Staehelin, L. A. (1987) J. Cell Biol. 105, 2257-2265].

Chloroplasts↗

PubMed1980

Stimulation of electron transport from photosystem II to photosystem I in spinach chloroplasts.

Electron transport from Photosystem II to Photosystem I of spinach chloroplasts can be stimulated by bicarbonate and various carbonyl or carboxyl compounds. Monovalent or divalent cations, which have hitherto been implicated in the energy distribution between the two photosystems, i.e., "spillover" phenomena at low light intensities, show a similar effect under high light conditions employed in this study. A mechanism for this stimulation of forward electron transport from Photosystem II to Photosystem I could involve inhibition of two types of Photosystem II partial reactions, which may involve cycling of electrons around Photosystem II. One of these is the DCMU-insensitive silicomolybdate reduction, and the other is ferricyanide reduction by Photosystem II at pH 8 in the presence of dibromothymoquinone. Greater stimulation of forward electron transport reactions is observed when both types of PHotosystem II cyclic reactions are inhibited by bicarbonate, carbonyl and carboxyl-type compounds, or by certain mono- or divalent cations.

Bicarbonates↗

PubMed1975

Evidence for energy migration from photosystem I to photosystem II and the effect of magnesium.

1. With Euglena chloroplasts 7722 nm light excites a fluorescence induction pattern, measured at l,u nm, typical of the Photosystem II reduction of Q. 2. Both methylviologen and phenazine methosulfate partially quench this fluorescence rise in the absence of electron transport between Photosystem II and Photosystem I, and in a manner consistent with their known role of stimulating Photosystem I photochemistry. 3. The variable fluorescence excited with 22 nm light is reduced to a greater extent than that excited by 638 nm light upon chlorophyll dilution during division in the dark. 4. These observations are interpreted to indicate that in Euglena chloroplasts light absorbed by Photosystem I is transferred energetically "uphill" to Photosystem II, where it can perform Photosystem II photochemistry. 5. Magnesium ions stimulate the variable fluorescence with both 638 nm and 722 nm light to a similar extent, which argues against the concept of magnesium ion interrupting energy transfer between Photosystem II and Photosystem I.

Chlorophyll↗

PubMed1976

A demonstration of energy transfer from photosystem II to photosystem I in chloroplasts.

Photosystem I activity of Tris-washed chloroplasts was measured at room temperature as the rate of photoreduction of NADP and as the rate of oxygen uptake mediated by methyl viologen in both cases using dichlorophenolindophenol plus ascorbate as the source of electrons for Photosystem I. With both assay systems the rate of electron transport by Photosystem I was stimulated approx. 20% by the addition of 3-(3,4-dichlorophenyl)-1,1-dimethylurea which caused the Photosystem II reaction centers to close. Photosystem I activity of chloroplasts was measured at low temperature as the rate of photooxidation of P-700. Chloroplasts suspended in the presence of hydroxylamine and 3-(3,4-dichlorophenyl)-1,1-dimethylurea were frozen to -196 degrees C after adaptation to darkness or after a preillumination at room temperature. The Photosystem II reaction centers of the frozen dark-adapted sample were all open; those of the preilluminated sample were all closed. The rate of photooxidation of P-700 at -196 degrees C with the preilluminated sample was approx. 25% faster than with the dark-adapted sample. We conclude from both the room temperature and the low temperature experiments that there is greater energy transfer from Photosystem II to Photosystem I when the Photosystem II reaction centers are closed and that these results are a direct demonstration of spillover.

Chloroplasts↗

PubMed1975

Diaminobenzidine an electron donor to photosystem 1 and to photosystem 2 in chloroplasts.

1. 3,3'-Diaminobenzidine was shown to serve as an electron donor to photosystem 1 in the presence of 3-(3,4-dichlorophenyl)-1,1-dimethylurea. In Tris-treated chloroplasts diaminobenzidine serves as an electron donor to photosystem 1 and to photosystem 2; the latter is sensitive to 3-(3,4-dichlorophenyl)-1,1-dimethylurea. 2. Addition of diaminobenzidine to Tris-treated chloroplasts causes an increase in fluorescence yield. 3. Diaminobenzidine-dependent electron transport mediated by photosystem 2 is coupled to synthesis of ATP even in the absence of an electron acceptor. This phosphorylation which is presumably supported by cyclic electron flow, is sensitive to 3-(3,4-dichlorophenyl)-1,1-dimethylurea. 4. Diaminobenzidine-dependent ATP formation, in Tris-treated chloroplasts exhibits the red-drop phenomenon. 5. The diaminobenzidine-induced cyclic photophosphorylation (mediated by photosystem 2) is resistant to a large extent to KCN-treatment which is known to inhibit reactions catalyzed by photosystem 1. On the other hand ATP formation supported by electron transport from diaminobenzidine to methyl viologen [in the presence of 3-(3,4-dichlorophenyl)-1,1-dimethylurea] is largely inhibited by KCN-treatment. This observation suggests that there are two coupling sites of ATP formation, one catalyzed by diaminobenzidine as a donor to photosystem 1 (in the presence of 3-(3,4-dichlorophenyl)-1,1-dimethylurea), and the other supported by diaminobenzidine which acts both as a donor to photosystem 2 (in Tris-treated chloroplasts) and as an acceptor (in its oxidized form) from a carrier located between the two photosystems.

3,3'-Diaminobenzidine↗

PubMed2006

Chlorophyll triplet states associated with Photosystem I and Photosystem II in thylakoids of the green alga Chlamydomonas reinhardtii.

The analysis of FDMR spectra, recorded at multiple emission wavelengths, by a global decomposition technique, has allowed us to characterise the triplet populations associated with Photosystem I and Photosystem II of thylakoids in the green alga Chlamydomonas reinhardtii. Three triplet populations are observed at fluorescence emissions characteristic of Photosystem II, and their zero field splitting parameters have been determined. These are similar to the zero field parameters for the three Photosystem II triplets previously reported for spinach thylakoids, suggesting that they have a widespread occurrence in nature. None of these triplets have the zero field splitting parameters characteristic of the Photosystem II recombination triplet observed only under reducing conditions. Because these triplets are generated under non-reducing redox conditions, when the recombination triplet is undetectable, it is suggested that they may be involved in the photoinhibition of Photosystem II. At emission wavelengths characteristic of Photosystem I, three triplet populations are observed, two of which are attributed to the P(700) recombination triplet frozen in two different conformations, based on the microwave-induced fluorescence emission spectra and the triplet minus singlet difference spectra. The third triplet population detected at Photosystem I emission wavelengths, which was previously unresolved, is proposed to originate from the antenna chlorophyll of the core or the unusually blue-shifted outer antenna complexes of this organism.

Animals↗

PubMed2002

Functional implications on the mechanism of the function of photosystem II including water oxidation based on the structure of photosystem II.

The structure of photosystem I at 3.8 A resolution illustrated the main structural elements of the water-oxidizing photosystem II complex, including the constituents of the electron transport chain. The location of the Mn cluster within the complex has been identified for the first time to our knowledge. At this resolution, no individual atoms are visible, however, the electron density of the Mn cluster can be used to discuss both the present models of the Mn cluster as revealed from various spectroscopic methods and the implications for the mechanisms of water oxidation. Twenty-six chlorophylls from the antenna system of photosystem II have been identified. They are arranged in two layers, one close to the stromal side and one close to the lumenal side. Comparing the structure of the antenna system of photosystem II with the chlorophyll arrangement in photosystem I, which was recently determined at 2.5 A resolution shows that photosystem II lacks the central domain of the photosystem I antenna, which is discussed in respect of the repair cycle of photosystem II due to photoinhibition.

Crystallography, X-Ray↗

PubMed1977

Photophosphorylation Associated with Photosystem II: III. Characterization of Uncoupling, Energy Transfer Inhibition, and Proton Uptake Reactions Associated with Photosystem II Cyclic Photophosphorylation.

A number of uncouplers and energy transfer inhibitors suppress photosystem II cyclic photophosphorylation catalyzed by either a proton/electron or electron donor. Valinomycin and 2,4-dinitrophenol also inhibit photosystem II cyclic photophosphorylation, but these compounds appear to act as electron transport inhibitors rather than as uncouplers. Only when valinomycin, KCl, and 2,4-dinitrophenol were added simultaneously to phosphorylation reaction mixtures was substantial uncoupling observed. Photosystem II noncyclic and cyclic electron transport reactions generate positive absorbance changes at 518 nm. Uncoupling and energy transfer inhibition diminished the magnitude of these absorbance changes. Photosystem II cyclic electron transport catalyzed by either p-phenylenediamine or N,N,N',N'-tetramethyl-p-phenylenediamine stimulated proton uptake in KCN-Hg-NH(2)OH-inhibited spinach (Spinacia oleracea L.) chloroplasts. Illumination with 640 nm light produced an extent of proton uptake approximately 3-fold greater than did 700 nm illumination, indicating that photosystem II-catalyzed electron transport was responsible for proton uptake. Electron transport inhibitors, uncouplers, and energy transfer inhibitors produced inhibitions of photosystem II-dependent proton uptake consistent with the effects of these compounds on ATP synthesis by the photosystem II cycle. These results are interpreted as indicating that endogenous proton-translocating components of the thylakoid membrane participate in coupling of ATP synthesis to photosystem II cyclic electron transport.

Journal Article↗

PubMed1990

Transcript Levels and Synthesis of Photosystem II Components in Cyanobacterial Mutants with Inactivated Photosystem II Genes.

After interruption or deletion of the photosystem II genes psbB, psbC, and psbD in the cyanobacterium Synechocystis sp. PCC 6803, thylakoids from such mutants were found to be depleted in a number of photosystem II proteins in addition to those for which the gene(s) had been inactivated. Transcript levels of photosystem II genes were measured and protein pulse-labeling was carried out to determine the reason for this effect. Transcripts of all photosystem II genes except the inactivated one(s) were found to be present in the various mutants. In certain cases, inactivation of one photosystem II gene led to overexpression of another. Protein pulse-labeling experiments using 35S-methionine, in which not only the rapidly turning over D1 protein but also D2, CP43, and CP47 appear to be preferentially labeled, showed that the mutants studied synthesize the D1 protein as well as other photosystem II proteins whose genes were not inactivated. The fact that, in the various mutants, photosystem II proteins for which the gene is not inactivated are synthesized but do not accumulate in the thylakoid indicates that the psbB, psbC, and psbD gene products are all required for a stable assembly of the photosystem II complex.

Journal Article↗

PubMed2006

Identification of Photosystem I and Photosystem II enriched regions of thylakoid membrane by optical microimaging of cryo-fluorescence emission spectra and of variable fluorescence.

Oxygenic photosynthesis of higher plants requires linear electron transport that is driven by serially operating Photosystem II and Photosystem I reaction centers. It is widely accepted that distribution of these two types of reaction centers in the thylakoid membrane is heterogeneous. Here, we describe two optical microscopic techniques that can be combined to reveal the heterogeneity. By imaging micro-spectroscopy at liquid nitrogen temperature, we resolved the heterogeneity of the chloroplast thylakoid membrane by distinct spectral signatures of fluorescence emitted by the two photosystems. With another microscope, we measured changes in the fluorescence emission yield that are induced by actinic light at room temperature. Fluorescence yield of Photosystem II reaction centers varies strongly with light-induced changes of its photochemical yield. Consequently, application of moderate background irradiance induces changes in the Photosystem II fluorescence yield whereas no such modulation occurs in Photosystem I. This contrasting feature was used to identify regions in thylakoid membranes that are enriched in active Photosystem II.

Image Processing, Computer-Assisted↗

PubMed2003

Molecular analysis of the Chlamydomonas nuclear gene encoding PsbW and demonstration that PsbW is a subunit of photosystem II, but not photosystem I.

PsbW is a nuclear-encoded protein located in the thylakoid membrane of the chloroplast. Studies in higher plants have provided substantial evidence that PsbW is a core component of photosystem II. However, recent data have been presented to suggest that PsbW is also a subunit of photosystem I. Such a sharing of subunits between the two photosystems would represent a novel phenomenon. To investigate this, we have cloned and characterized the psbW gene from the green alga Chlamydomonas reinhardtii. The gene is split by five introns and encodes a polypeptide of 115 residues comprising the 6.1 kDa mature PsbW protein preceded by a 59 amino acid bipartite transit sequence. Using antibodies raised to PsbW we have examined: (1) C. reinhardtii mutants lacking either photosystem and (2) purified photosystem preparations. We find that PsbW is a subunit of photosystem II, but not photosystem I.

Algal Proteins↗