The P700-chlorophyll -protein of a blue-green alga

Biosynthesis of the photosystem I chlorophyll-protein complex in greening leaves of higher plants

Biosynthesis of photosystem I chlorophyll-protein complex, derived from chloroplast lamellae solubilized with Triton X-100, was examined in rapidly greening primary leaves of the jack bean. It was found that the chlorophyll/P700 ratio of the complex was low (35/1) in the early stages of greening, and increased steadily to a stable level (75/1) during continued chloroplast development. It is suggested from these results that in the initial stages of greening, and probably throughout synthesis, the P700-chlorophyll-protein molecules are first inserted into the developing lamellae, and those photosystem I chlorophyll-protein molecules functioning solely in a light-harvesting capacity are added subsequently.

Higher plant chloroplasts: Evidence that all the chlorophyll exists as chlorophyll-protein complexes

By using the polyacrylamide gel electrophoresis system described in this report, it was possible to fractionate all the photosynthetic pigments of maize (Zea mays L.) thylakoids into chlorophyll-protein complexes with negligible formation of free or detergent-complexed chlorophyll. Identical sodium dodecyl sulfate extracts of thylakoids have previously resulted in up to 50% of the chlorophyll migrating as free chlorophyll after electrophoresis. The major difference from previous gel electrophoresis systems is the replacement of sodium dodecyl sulfate in the electrophoresis buffer by Deriphat 160 (disodium N-lauryl-beta-iminodipropionate), a zwitterionic detergent. The results suggest that: (i) no significant amount of free chlorophyll exists in the chloroplast thylakoid membranes in vivo, and (ii) most of the free pigment seen previously on gels was generated during the electrophoresis and was not a result of the solubilization technique. Additionally, the new chlorophyll-protein complexes resolved appear to have different characteristics (pigment content and size) that those observed in former systems.

Thirty years of fun with antenna pigment-proteins and photochemical reaction centers: A tribute to the people who have influenced my career

The author summarizes the research contributions to photosynthesis made by him, his graduate and postdoctoral students, visiting scientists and by his collaboration with other photosynthesis workers during 1964-1994. The development of isolation procedures and biochemical/biophysical characterization of antenna pigment-proteins and photochemical reaction centers are described together with the author's education and experiences as a scientific researcher. Some anecdotes hopefully add insight into what it was like to be in this area of science during the period.

Comparison of the electron spin polarized spectrum found in plant photosystem I and in iron-depleted bacterial reaction centers with time-resolved K-band EPR; evidence that the photosystem I acceptor A1 is a quinone

The suggestion that the electron acceptor A1 in plant photosystem I (PSI) is a quinone molecule is tested by comparisons with the bacterial photosystem. The electron spin polarized (ESP) EPR signal due to the oxidized donor and reduced quinone acceptor (P 870 (+) Q(-)) in iron-depleted bacterial reaction centers has similar spectral characteristics as the ESP EPR signal in PSI which is believed to be due to P 700 (+) A 1 (-) , the oxidized PSI donor and reduced A1. This is also true for better resolved spectra obtained at K-band (∼24 GHz). These same spectral characteristics can be simulated using a powder spectrum based on the known g-anisotropy of reduced quinones and with the same parameter set for Q(-) and A1 (-). The best resolution of the ESP EPR signal has been obtained for deuterated PSI particles at K-band. Simulation of the A1 (-) contribution based on g-anisotropy yields the same parameters as for bacterial Q(-) (except for an overall shift in the anisotropic g-factors, which have previously been determined for Q(-)). These results provide evidence that A1 is a quinone molecule. The electron spin polarized signal of P700 (+) is part of the better resolved spectrum from the deuterated PSI particles. The nature of the P700 (+) ESP is not clear; however, it appears that it does not exhibit the polarization pattern required by mechanisms which have been used so far to explain the ESP in PSI.

Sequence of two genes in pea chloroplast DNA coding for 84 and 82 kD polypeptides of the photosystem I complex

The genes encoding the two P700 chlorophyll a-apoproteins of the photosystem I complex were localized on the pea (Pisum sativum) chloroplast genome. The nucleotide sequence of the genes and the flanking regions has been determined. The genes are separated by 25 bp and are probably cotranscribed. The 5' terminal gene (psaA1) codes for a 761-residue protein (MW 84.1 kD) and the 3' terminal gene (psaA2) for a 734-residue protein (MW 82.4 kD). Both proteins are highly hydrophobic and contain eleven putative membrane-spanning domains. The homology to the corresponding polypeptides from maize are 89% and 95% for psaA1 and psaA2, respectively. A putative promoter has been identified for the psaA1 gene, and potential ribosome binding sites are present before both genes.

Multiple forms of P700-chlorophyll a-protein complexes from Synechococcus sp.: The iron, quinone and carotenoid contents

The iron, quinone and carotenoid contents of five P700-chlorophyll a-protein complexes having different subunit structures (CP1-a,-b,-c,-d and-e) from the thermophilic cyanobacterium Synechococcus sp. were determined. CP1-a,-b,-c and-d that commonly have four polypeptides of 62,000, 60,000, 14,000 and 10,000 dalton contained 10-14 iron atoms per P700, whereas CP1-e that lacks the two small polypeptides was totally devoid of iron. All CP1 complexes contained vitamin K1 at the molar ratio of vitamin K1 to P700 of about 2 except CP1-e that had only 0.4 vitamin K1 per P700. No plastoquinone was detected in five CP1 complexes. Out of four major carotenoids, β-carotene, zeaxanthin, caloxanthin, and myxoxanthophyll, present in the thylakoid membranes, only β-carotene was found in isolated CP1 complexes; all CP1 complexes contained about 10 β-carotene molecules per P700. The flourescence excitation spectrum showed that β-carotene serves as an efficient antenna of photosystem I. It is concluded that all iron atoms and a larger fraction of vitamin K1 molecules present in the photosystem I reaction center complex are associated with the 14,000 and 10,000 dalton polypeptides, whereas β-carotene exclusively binds to the large polypeptides which carry the functional and antenna chlorophyll a. The possible functions of iron and vitamin K1 as electron carriers and of β-carotene as the accessary pigment and a photoprotectant in the photosystem I complexes are discussed.

Partial characterization of six chlorophyll a-protein complexes isolated from a blue-green alga by a nondetergent method

The chlorophyll a-protein complexes of a blue-green alga, Phormidium luridum, are resolved in the absence of detergent, by the combination of a Sepharose 4B column and sucrose density gradient centrifugation, into six chlorophyll a-containing zones. These six complexes are termed here as F15, F25, F35, F40, F60, and F65, according to their appearance in the sucrose density gradient after centrifugation. The absorption spectra of these six isolated complexes are reported, as well as the fluorescence emission spectra at room temperature and liquid-nitrogen temperature. The F60 complex was enriched in Photosystem I, while the F35 and F40 complexes contained both Photosystem I and II. The F60 complex is the predominant band and accounts for about 49% of the total chlorophyll a of the cells. The extinction coefficient of this complex is determined to be 68.7 mM-1 cm-1 at 680 nm in 50 mM tris(hydroxymethyl)amino methane buffer at pH 8.0. In addition, the effect of the detergent, sodium dodecyl sulfate, on these spectra are also reported for comparison. The chemically induced difference spectra of F35, F40, and F60 complexes also indicate the presence of the reaction center, P700, of Photosystem I. These three complexes have been shown to contain P700 in a ratio of approximately one reaction center molecule per 100 light-harvesting chlorophyll molecules. The simple exposure of the F60 fraction to sodium dodecyl sulfate results in an "apparent" enhancement of the P700 to chlorophyll ratio to one P700 per 51 light harvesting chlorophyll. Room temperature electron spin resonance measurements of photooxidized F60 are consistent with the presence of P700 and with the chlorophyll/P700 ratio observed by chemical assay. The amino acid compositions of F60 and F65 complexes are studied. Gel electrophoresis patterns of these six isolated complexes are presented and are significantly different from those reported for detergent-treated chlorophyll-protein complexes.

Chiroptical properties of chlorophyll-protein complexes separated on Deriphat/polyacrylamide gel

Circular dichroism (c.d.) was measured for four chlorophyll-protein complexes, resolved from sodium dodecyl sulphate extracts of chloroplasts by electrophoresis in polyacrylamide gel containing Deriphat 160 (disodium N-dodecyl beta-imidopropionate), a zwitterionic detergent. The slowest-band (1) complex was found to be identical with the complex CP1 as found on electrophoresis in the presence of anion detergent, but it was in a much higher yield (30% of the chlorophyll a). In band-2 and -3 protein complexes a c.d. pattern described for the complex CP2 could be recognized. Another c.d. component of a split-exciton type with extrema at 680 (-) and 669 (+)nm, together with evidence of disorganized chlorophyll, was found in band-2, -3 and -4 complexes. When a barley (Hordeum vulgare) mutant lacking chlorophyll b was examined, only bands 1 and 4 were obtained, and the c.d. of the band-4 complex was much less affected by disorganized chlorophyll. C.D. spectra resembling that of this band-4 complex could be generated by subtracting the c.d. of complex CP1 from the c.d. of photochemically active mutant chloroplast fragments, or by subtracting the c.d. of complexes CP1 and CP2 from pea (Pisum sativum) chloroplast fragments. The Deriphat appears to have preserved at least to some extent a new type of chlorophyll a-protein complex.

Contribution to the structural characterization of eucaryotic PSI reaction centre - II. Characterization of a highly purified photoactive SDS-CP1 complex

Under precise conditions, SDS PAGE† allows purification of a photoactive P700-chla-protein complex from eucaryotic cells. The yield of P700 recovery is close to 100%. A total protein content equivalent to about 140 kD for one mole of P700 has been estimated by chemical analysis, and electrophoresis revealed the presence of two peptidic chains with MWs close to 65 kD. Photochemical and structural properties of this complex are given and compared with those of other complexes previously isolated.

Isolation and characterization of photosystem I and II membrane particles from the blue-green alga, Synechococcus cedrorum

Fractions enriched in either Photosystem I or Photosystem II activity have been isolated from the blue-green alga, Synechococcus cedrorum after digitonin treatment. Sedimentation of this homogenate on a 10--30% sucrose gradient yielded three green bands: the upper band was enriched in Photosystem II, the lowest band was enriched in Photosystem I, while the middle band contained both activities. Large quantities of both particles were isolated by zonal centrifugation, and the material was then further purified by chromatography on DEAE-cellulose. The resulting Photosystem II particles carried out light-induced electron transport from semicarbizide to ferricyanide of over 2000 mumol/mg Chlorophyll per h (which was sensitive to 3-(3,4-dichlorophenyl)-1, 1-dimethylurea), and was nearly devoid of Photosystem I activity. This particle contains beta-carotene, very little phycocyanin, has a chlorophyll absorption maximum at 675 nm, and a liquid N2 fluorescence maximum at 685 nm. The purest Photosystem II particles have a chlorophyll to cytochrome b-559 ratio of 50 : 1. The Photosystem I particle is highly enriched in P-700, with a chlorophyll to P-700 ratio of 40 : 1. The physical structure of the two Photosystem particles has also been studied by gel electrophoresis and electron microscopy. These results indicate that the size and protein composition of the two particles are distinctly different.

Composition of a photosystem I chlorophyll protein complex from Anabaena flos-aquae

The use of Triton X-100 to solubilize membrane fragments from Anabaena flos-aquae in conjunction with DEAE cellulose chromatography allows the separation of three green fractions. Fraction 1 is detergent-solubilized chlorophyll, and Fraction 2 contains one polypeptide in the 15 kdalton area. Fraction 3, which contains most of the chlorophyll and shows P-700 and photosystem I activity, shows by SDS gel electrophoresis varying polypeptide profiles which reflect the presence of four fundamental bands as well as varying amounts of other polypeptides which appear to be aggregates containing the 15 kdalton polypeptide. The four fundamental bands are designated Band I at 120, Band II at 52, Band III at 46, and Band IV at 15 kdaltons. Band I obtained using 0.1% SDS contains chlorophyll and P-700 associated with it. When this band is cut out and rerun, the 120 kdalton band is lost, but significant increases occur in the intensities of Bands II, III, and IV as well as other polypeptides in the 20-30 kdalton range. The use of 1% Triton X-100 coupled with sucrose density gradient centrifugation allows the separation of three green bands at 10, 25 and 40% sucrose. The 10% layer contains a major polypeptide which appears to be Band IV. The 25 and 40% layers show essentially similar polypeptide profiles, resembling Fraction 3 in this regard, except that the 40% layer shows a marked decrease in Band III. Treatment of the material layering at the 40% sucrose level with a higher (4%) concentration of Triton X-100 causes a loss (disaggregation) of the polypeptides occurring in the 60-80 kdalton region and in increase in the lower molecular weight polypeptides. Thus, aggregation of the lower molecular weight polypeptides accounts for the variability seen in the electrophoresis patterns. Possible relations of the principal polypeptides to the known photochemical functions in the original membrane are discussed.

PRoperties of the low-temperature photosystem I primary reaction in the P-700-chlorophyll alpha-protein

The Photosystem I primary reaction, as measured by electron paramagnetic resonance changes of P-700 and a bound iron-sulfur center, has been studied at 15 degrees K in P-700-chlorophyll alpha-protein complexes isolated from a blue-green alga. One complex, prepared with sodium dodecyl sulfate shows P-700 photooxidation only at 300 degrees K, whereas a second complex, prepared with Triton X-100, is photochemically active at 15 degrees K as well as at 300 degrees K. Analysis of these two preparations shows that the absence of low-temperature photoactivity in the sodium dodecyl sulfate complex reflects a lack of bound iron-sulfur centers in this preparation and supports the assignment of an iron-sulfur center as the primary electron acceptor of Photosystem I.

A chlorophyll-protein complex lacking in photosystem I mutants of Chlamydomonas reinhardtii

Sodium dodecyl sulfate gel electrophoresis of unheated, detergent-solubilized thylakoid membranes of Chlamydomonas reinhardtii gives two chlorophyll-protein complexes. Chlorophyll-protein complex I (CP I) is the blue-green in color and can be dissociated by heat into "free" chlorophyll and a constituent polypeptide (polypeptide 2; mol wt 66,000). Similar experiments with spinach and Chinese cabbage show that the higher plant CP I contains an equivalent polypeptide but of slightly lower molecular weight (64,000). Both polypeptide 2 and its counterpart in spinach are soluble in a 2:1 (vol/vol) mixture of chloroform-methanol. Chemical analysis reveals that C. reinhardtii CP I has a chlorophyll a to b weight ratio of about 5 and that it contains approximately 5% of the total chlorophyll and 8-9% of the total protein of the thylakoid membranes. Thus, it can be calculated that each constituent polypeptide chain is associated with eight to nine chlorophyll molecules. Attempts to measure the molecular weight of CP I by calibrated SDS gels were unsuccessul since the complex migrates anomalously in such gels. Two Mendelian mutants of C. reinhardtii, F1 and F14, which lack P700 but have normal photosystem I activity, do not contain CP I or the 66,000-dalton polypeptide in their thylakoid membranes. Our results suggest that CP I is essential for photosystem I reaction center activity and that P700 may be associated with the 66,000-dalton polypeptide.

Properties of protein-chlorophyll complexes from pea (Pisum sativum L.) leaves. The organization of chlorophyll

Chlorophyll-protein-detergent complexes were prepared from pea chloroplasts by using sodium dodecylbenzenesulphonate and polyacrylamide-gel electrophoresis. Circular-dichroism spectra showed that complex CPI has a dimeric arrangement of chlorophyll a, with additional weaker interactions. Ellipticities were determined for both complexes and for purified chlorophylls in solution, and it is argued that the circular dichroism of complex CPII is derived from chlorophyll-protein interaction rather than from interaction between chlorophylls a and b. The detergent could be removed from the complexes by using urea and gel filtration, leaving the chlorophyll-protein in solution, although in each case a diminished ellipticity indicated some loss of organization. Three-peaked circular-dichroism spectra of chloroplast fragments before and after addition of detergent were compared with a curve obtained by summing graphically the spectra of complexes CPI, CPII and the free-pigment fraction. There was good correspondence at 650 nm, and the longer-wavelength peaks agreed in form and magnitude, but with discrepancies in position. It was concluded that complexes CPI and CPII pre-exist in the original material, but that there is an environmental effect which is destroyed when the complexes are extracted.

Synthesis of chloroplast membrane polypeptides during synchronous growth of Chlamydomonas reinhardtii

The synthesis of the major chloroplast membrane polypeptides has been studied during synchronous growth of Chlamydomonas reinhardtii. Under these conditions, chlorophyll is synthesized during the latter part of the light period and cell division takes place during the dark period. The profile of the chloroplast membrane polypeptides of C. reinhardtii has been well characterized and shown to contain two major classes by size (Hoober, J. 1970. J. Biol. Chem.245:4327). Polypeptides of group I have a mol wt range of 50,000-55,000 daltons. The second region consists of at least three polypeptide groups, IIa, IIb, and IIc, having mol wt of 40,000, 31,000, and 27,000 daltons, respectively. The synthesis of these polypeptides has been measured using a double-labeling technique and a computer-aided statistical analysis. The rate of labeling of group I polypeptides is highest during the early light period and decreases after 6 h of growth. Group IIa is labeled from the beginning of the light period, but little synthesis of IIb occurs before 3 h, and significant amounts of label are not found in IIc before 5 h of growth. After approximately 8 h of light, groups IIb and IIc are synthesized at rates significantly greater than those of the other membrane polypeptides. The synthesis of the major polypeptide groups ceases in the dark. We conclude that the biosynthesis of the chloroplast membranes is a sequential or stepwise process.

Composition and activity of the photosynthetic apparatus in temperature-sensitive mutants of higher plants

Six nuclear mutants of corn, six of soybean, and seven of cotton displayed low temperature-induced virescence when grown in controlled environments. For the group of plants studied, an increase in leaf chlorophyll a/b ratio was correlated with a temperature-sensitive biosynthetic sequence leading to a reduction in total chlorophyll content. These pigment alterations were reflected in the composition and quantity of the two major chlorophyll-protein complexes of chloroplast membranes. Changes in the amount of the major light-harvesting chlorophyll-protein complex was a prime consequence of the nuclear mutations. A decrease in the light-harvesting chlorophyll component of the light reaction centers of the leaf may account for the decrease in size of the photo-synthetic unit frequently noted in chlorophyll-deficient mutants. Variations in the concentration of the chlorophyll-protein complexes in the chloroplast lamellae may be causally related to variations in CO(2) compensation points of mutant soybean and cotton plants.

Primary photochemical reactions in chloroplast photosynthesis

Photosynthesis begins with the absorption of light energy and this absorbed energy is transferred to special sites, termed reaction centres. At these sites, the light energy is transformed into chemical products through an oxidation-reduction reaction that generates the primary reactants, an oxidized pigment molecule (P+) and a reduced electron acceptor (A–) (Clayton, 1972). The subsequent reactions of these species in the dark ultimately results in the formation of chemical products required for the fixation of CO2. In this essay we will discuss the nature of the primary reactants generated in the light reactions of chloroplast photosynthesis, stressing recent advances in the identification and characterization of such reactants.

Physiology and cytological chemistry blue-green algae

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