Absorption and fluorescence spectra of chlorophyll-proteins isolated from Euglena gracilis

A spectroscopic study of chlorophyll-protein complexes isolated from Euglena gracilis membranes was carried out to gain information about the state of chlorophyll in vivo and energy transfer in photosynthesis. The membranes were dissociated by Triton X-100 and separated into fractions by sucrose gradient centrifugation and hydroxyapatite chromatography. Four different types of chlorophyll-protein complexes were distinguished from each other and from detergent-solubilized chlorophyll in these fractions by examination of their absorption, fluorescence excitation (400–500 nm) and emission spectra at low temperature. These types were: (1). A mixture of antenna chlorophyll a- and chlorophyll ab-proteins with an absorption maximum at 669 and emission at 682 nm; (2) a P-700-chlorophyll a-protein (chlorophyll: P-700 = 30 : 1), termed CPI with an absorption maximum at 676 nm and emission maxima at 698 and 718 nm; (3) a second chlorophyll a-protein (CPI-2) less enriched in P-700, with an absorption maximum at 676 nm and emission maxima at 680, 722 and 731 nm; (4) a third chlorophyll a-protein (CPa₁) with no P-700, absorption maxima at 670 and 683 nm, and an unusually sharp emission maximum at 687 nm. Treatment of CPa₁ with sodium dodecyl sulfate drastically altered its spectroscopic properties indicating that at least some chlorophyll-proteins isolated with this detergent are partially denatured. The results suggest that the complex absorption spectra of chlorophyll in vivo are caused by varying proportions of different chlorophyll-protein complexes, each with different groups of chlorophyll molecules bound to it and making up a unique entity in terms of electronic transitions.     

The electrophoretic isolation and partial characterization of three chlorophyll-protein complexes from blue-green algae

Three chlorophyll-protein complexes have been resolved from blue-green algae using an improved procedure for membrane solubilization and electrophoretic fractionation. One complex has a red absorbance maximum of 676 nm and a molecular weight equivalency of 255 000 ± 15 000. A second complex has an absorbance maximum of 676 nm, a molecular weight equivalency of 118 000 ± 8000, and resembles the previously described P-700-chlorophylla-protein (CPI) of higher plants and algae. The third chlorophyll-protein has a red absorbance maximum of 671 nm and a molecular weight equivalency of 58 000 ± 5000. Blue-green algal membrane fractions enriched in Photosystem I and heterocyst cells do not contain this third chlorophyll-protein, whereas Photosystem II-enriched membrane fractions and vegetative cells do. A component of the same spectral characteristics and molecular weight equivalency was also observed in chlorophyll b-deficient mutants of barley and maize. It is hypothesized that this third complex is involved in some manner with Photosystem II.     

Properties of light-harvesting chlorophyll a/b-protein, and photosystem I chlorophyll a-protein, purified from digitonin extracts of spinach chloroplasts by isoelectrofocusing

A procedure for purifying both light-harvesting chlorophylla/b-protein and photosystem I chlorophyll -protein from digitoninextracts of spinach chloroplasts is described. This procedureuses isoelectrofocusing on Ampholine at the last step and permitsisolating all of the chlorophyll-proteins from the same extractin a better yield and a highly pure state. The purified light-harvesting chlorophyll a/b-protein whichhas an isoelectric point (pi) of 4.35 (?0.1) and a single polypeptideof 24 kilodaltons (kD), shows slightly higher chlorophyll a/Aratio of 1.35 than the values reported for the preparationsobtained by anionic detergents. This chlorophyll-protein exhibitsa markedly high and sharp fluorescence band at 681 nm at 77?Kwhich is not found on the chloroplast emission spectrum. Photosystem I chlorophyll a-protein focuses on Ampholine intotwo bands with pi values of 4.75 (?0.1) and 4.80 (?0.1). Thesetwo fractions show the same absorption spectra (maximum at 678nm at room temperature) and emission spectra (maximum at 734nm at 77?K) and have the same constituent polypeptides: onelarge band at 55–64 kD and six minor bands (21.5, 20,19, 18, 16 and 15 kD). The polypeptide composition and the P-700to chlorophyll a ratio (1 to ca. 80) of this preparation arevery similar to those of the photosystem I reaction center preparationobtained from Swiss chard chloroplasts by Bengis and Nelson(8). (Received October 31, 1978; )     

Euploidy in Ricinus: EUPLOIDY EFFECTS ON PHOTOSYNTHETIC ACTIVITY AND CONTENT OF CHLOROPHYLL-PROTEINS

The effects of nuclear genome duplication on the chlorophyll-protein content and photochemical activity of chloroplasts, and photosynthetic rates in leaf tissue, have been evaluated in haploid, diploid, and tetraploid individuals of the castor bean, Ricinus communis L. Analysis of this euploid series revealed that both photosystem II (2,6-dichlorophenolindophenol reduction) and photosystem I oxygen uptake (N,N,N′,N′-tetramethyl-p-phenylenediamine to methyl viologen) decrease in plastids isolated from cells with increasingly larger nuclear complement sizes. Photosynthetic O₂-evolution and ¹⁴CO₂-fixation rates in leaf tissue from haploid, diploid, and tetraploid individuals were also found to decrease with the increase in size of the nuclear genome. Six chlorophyll-protein complexes, in addition to a zone of detergent complexed free pigment, were resolved from sodium dodecyl sulfate-solubilized thylakoid membranes from cells of all three ploidy levels. In addition to the P700-chlorophyll a-protein complex and the light-harvesting chlorophyll a/b-protein complex, four minor complexes were revealed, two containing only chlorophyll a and two containing both chlorophyll a and b. The relative distribution of chlorophyll among the resolved chlorophyll-protein complexes and free pigment was found to be similar for all three ploidy levels.     

Effects of Season and Low Temperature on Polypeptides from Thylakoids Isolated from Chloroplasts of Pinus silvestris

Thylakoids isolated from pine chloroplasts were solubilized by sodium dodecyl sulphate and the polypeptides were separated by polyacrylamide gel electrophoresis. The chlorophyll-protein complexes, P700-CPa₁ and LH-CPa/b, had apparent molecular weights of 92,000 and 25,000, respectively. When the chlorophyll of P700-CPa₁ was extracted or photobleached, the apoprotein of P700-CPa₁ appeared as a pronounced peak in the polypeptide scan profile. The molecular weight of the apoprotein was 70,000. During autumn and winter the complex P700-CPa₁ was destroyed. This was primarily caused by bleaching of chlorophyll, as the 70,000 apoprotein increased in the scan profile when the complex P700-CPa₁ decreased. The winter destruction of P700-CPa₁ was less pronounced in old needles than in young. Freezing of frost-hardened seedlings did not change the polypeptide scan profile, unless the temperature was lowered below the frost-killing point followed by thawing and post-treatment in light or darkness above 0°C. Again the main destruction occurred in the P700-CPa₁ complex, but in this case no significant increase of the apoprotein was observed. These alterations in the polypeptide scan profile of frost-killed needles were not caused by the low temperature treatment as such, but they occurred after thawing of the needles.     

Chlorophyll-protein complexes from higher plants: A procedure for improved stability and fractionation

An improved procedure for the electrophoretic fractionation of higher plant chlorophyllprotein complexes is described. Compared with currently used systems, it greatly reduces the amount of chlorophyll that is found unassociated with protein after electrophoresis and resolves four chlorophyll-protein complexes. The slowest migrating band has a red adsorption maximum at 674 nm or greater, contains chlorophyll a but not chlorophyll b, and has a molecular weight equivalency of 110,000. These properties are similar to the previously described CPI or P700-chlorophyll a-protein complex. The amount of the total chlorophyll in this material is increased by two to three fold over that present in the equivalent complex fractionated by previous procedures. The other three chlorophyll-protein complexes contain both chlorophylls a and b, and have molecular weight equivalencies of 80,000, 60,000, and 46,000. None of these complexes seems to correspond directly to the previously characterized light-harvesting chlorophyll $\text{a}\text{b}$-protein complex.     

Isolation of the light-harvesting chlorophyll a/b--protein complex from thylakoid membranes of barley by adsorption chromatography on controlled-pore glass.

The light-harvesting chlorophyll $\text{a}\text{b}$-protein complex has been isolated from barley thylakoids by a rapid, single-step procedure involving adsorption chromatography on controlled-pore glass columns. The Triton X-100-solubilized complex contains a polypeptide of apparent molecular weight, 26,000; the 0.25% Triton X-100 light-harvesting chlorophyll $\text{a}\text{b}$-protein has spectral characteristics consistent with its assumed in vivo state. On the same column free chlorophyll and carotenoids have been separated from chlorophyll-protein complex 1, but this complex contained many polypeptides other than those associated with chlorophyll. This method is potentially suitable for the isolation of other thylakoid membrane proteins. It may also be generally applicable for fractionation of intrinsic membrane proteins from other sources and for separation of mixed Triton X-100-lipid micelles.     

Chlorophyll-Protein Complexes of the Cyanophyte, Nostoc sp

Four chlorophyll-protein complexes have been resolved from the cyanophyte, Nostoc sp., by sodium dodecyl sulfate (SDS) polyacrylamide gel electrophoresis at 4 C. Complexes solubilized by SDS from Spinacia oleracea were run for comparison. As has been well documented, the P700-chlorophyll a-protein complex from the higher plant and blue-green algal samples are similar, and the light-harvesting pigment protein complex is present only in the former. Most noteworthy are two closely migrating chlorophyll proteins in Nostoc sp. which have approximately the same mobility as a single chlorophyll-protein band resolvable from spinach. The absorption maximum of the complex from spinach is at 667 nanometers, and those of the two complexes from Nostoc sp. are at 667 and 669 nanometers; the fluorescence emission maximum at −196 C is at 685 nanometers, and the 735 nanometer fluorescence peak, characteristic of the P700-chlorophyll a-protein complex, is absent. The apoproteins of these new complexes from Nostoc sp. and spinach are in the kilodalton range. It appears that at least one of these two chlorophyll-protein complexes from Nostoc sp. compares with those recently described by others from higher plants and green algae as likely photosystem II complexes, perhaps containing P680, although no photochemical data are yet available.     

Isolation and Characterization of a Light-Harvesting Chlorophyll a/b Protein Complex Associated with Photosystem I

A chlorophyll a/b protein complex has been isolated from a resolved native photosystem I complex by mildly dissociating sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The chlorophyll a/b protein contains a single polypeptide of molecular weight 20 kilodaltons, and has a chlorophyll a/b ratio of 3.5 to 4.0. The visible absorbance spectrum of the chlorophyll a/b protein complex showed a maximum at 667 nanometers in the red region and a 77 K fluorescence emission maximum at 681 nanometers. Alternatively, by treatment of the native photosystem I complex with lithium dodecyl sulfate and Triton, the chlorophyll a/b protein complex could be isolated by chromatography on Sephadex G-75. Immunological assays using antibodies to the P₇₀₀-chlorophyll a-protein and the photosystem II light-harvesting chlorophyll a/b protein show no cross-reaction between the photosystem I chlorophyll a/b protein and the other two chlorophyll-containing protein complexes.     

The reconstitution of a Photosystem II protein complex, P-700-chlorophyll a-protein complex and light-harvesting chlorophyll ab-protein

A Photosystem II reaction centre protein complex was extracted from spinach chloroplasts using digitonin. This complex showed (i) high rates of dichloroindophenol and ferricyanide reduction in the presence of suitable donors, (ii) low-temperature fluorescence at 685 nm with a variable shoulder at 695 nm which increased as the complex aggregated due to depletion of digitonin and (iii) four major polypeptides of 47, 39, 31 and 6 kDa on dissociating polyacrylamide gels. The Photosystem II protein complex, together woth the P-700-chlorophylla protein complex and light-harvesting chlorophyll $\text{a}\text{b-}\text{protein}$ complex (LHCP) also isolated using digitonin, were reconstituted with lipids from spinach chloroplasts to form proteoliposomes. The low-temperature (77 K) fluorescence properties of the various proteoliposomes were analysed. The $\text{F}{}_{685}\text{F}{}_{695}$ ratios of the Photosystem II reaction centre protein complex-liposomes decreased as the lipid to protein ratios were increased. The $\text{F}{}_{681}\text{F}{}_{697}$ ratios of LHCP-liposomes were found to behave similarly. Light excitation of chlorophyll b at 475 nm stimulated emission from both the Photosystem II protein complex (F₆₈₅ and F₆₉₅) and the P-700-chlorophyll a-protein complex (F₇₃₅) when LHCP was reconstituted with either of these complexes, demonstrating energy transfer between LHCP and PS I or II complexes in liposomes. No evidence was found for energy transfer from the PS II complex to the P-700-chlorophyll a-protein complex reconstituted in the same proteoliposome preparation. Proteoliposome preparations containing all three chlorophyll-protein complexes showed fluorescence emission at 685, 700 and 735 nm.     

Spectral characterization of five chlorophyll-protein complexes

Sodium dodecyl sulfate-solubilized chloroplast internal membranes of higher plants (cowpea [Vigna unguiculata L. Walp], chinese cabbage [Brassica chinensi L.], and tobacco [Nicotiana tabacum L.]) are resolved by polyacrylamide gel electrophoresis into two chlorophyll a- and three chlorophyll a,b-proteins. A small portion (about 15%) of the membrane chlorophyll migrates as a component of high electrophoretic mobility and presumably consists of detergent-complexed, protein-free pigment.

One of the chlorophyll a-proteins is qualitatively similar to the P₇₀₀ chlorophyll a-protein but contains a much larger proportion of total chlorophyll (about 30%) than previously reported. The second chlorophyll a-protein is a recently discovered component of the membrane and accounts for about 7% of the total chlorophyll. The absorption and fluorescence emission spectra of these two chlorophyll a-proteins differ.

The three chlorophyll a,b-proteins are components of the chloroplast membrane chlorophyll a,b-light-harvesting complex which was previously resolved as a single chlorophyll-protein band. The two additional chlorophyll a,b-proteins observed in our work probably represent larger aggregates contained within that membrane complex which are preserved under the solubilization and electrophoretic conditions used here.

     

CHARACTERIZATION OF PHOTOSYSTEM I-ASSOCIATED POLYPEPTIDES FROM THE CHLOROPHYLL b-RICH ALGA TETRASELMIS SPP. (PLEURASTROPHYCEAE) AND OTHER CHLOROPHYTE ALGAE1

The phylogenetic distribution of photosystem I-associated polypeptides was assessed by immunoblotting algal thylakoid membrane polypeptides with antisera generated against the P700-chlorophyll a protein (CC I) and a photosystem I light-harvesting chlorophyll-protein (LHC Ib). Polypeptides cross-reacting with the CC I apoprotein were found in 20 species representing four classes of unicellular algae. Polypeptides sharing antigenicity with spinach LHC Ib were observed only in algal species containing chlorophyll b. Tetraselmis spp. (Pleurastrophyceae), rich in chlorophyll b (Chl a:b 1.2), exhibited marked heterogeneity in the composition of their CC I and LHC Ib cross-reactive polypeptides. When immunoblotted with antisera against CC I, all Tetraselmis clones examined exhibited a 25-kD polypeptide in greater abundance than the 58-kD CC I apoprotein characteristic of higher plants and other green algal thylakoids. Three Tetraselmis clones (RG 6, RG 11, and RG 12) exhibited an 81-kD polypeptide with strong antigenicity toward the LHC Ib antisera, in contrast to the 17- to 24-kD cross-reactive polypeptides found in spinach, green algae, and one Tetraselmis clone (RG 5). Associated with the unique photosystem I polypeptide composition in Tetraselmis spp., Chl: P700 ratios for the group are 2–5 times greater than those observed for higher plants or other green algae. The chlorophyll b enrichment, unusual composition of photosystem I cross-reactive polypeptides, and heterogeneity of these polypeptides within isolates of Tetraselmis might make this genus useful for investigations of the functional organization of chlorophyll b in light-harvesting systems. These features also support the view of an alternative phyletic origin for the Pleurastrophyceae.     

Effects of Water Stress on Chlorophyll-Protein Complexes in Wheat Chloroplasts

The excitation energy transfer from light harvesting chlorophyll protein complexes to PS Ⅱ was inhibited under water stress. The contents of iriternal antennae chlorophyll-protein complexes of PS Ⅱ (CPa), light harvesting chlorophyll-protein complexes of PS Ⅱ (LHC Ⅱ ), light harvesting chlorophyll-protein of PS Ⅰ (LHC Ⅰ ) and chlorophyll a protein complex of reaction center of PS Ⅰ were decreased by water stress. The decrease of chlorophyll-protein complexes of PS Ⅱ was greater than that of PS Ⅰ . It was indicated that the amount of 25 kD polypeptide of LHC Ⅱ in particular, as well as that of 43 and 47 kD polypeptides of CPa, and 21 kD polypeptide of LHC Ⅰ , were reduced by water stress.     

Regulation of synthesis of the photosystem I reaction center

The in vivo biosynthesis of the P700 chlorophyll a-apoprotein was examined to determine whether this process is light regulated and to determine its relationship to chlorophyll accumulation during light- induced chloroplast development in barley (Hordeum vulgare L.). Rabbit antibodies to the 58,000-62,000-mol-wt apoprotein were used to measure relative synthesis rates by immunoprecipitation of in vivo labeled leaf proteins and to detect apoprotein accumulation on nitrocellulose protein blots. 5-d-old, dark-grown barley seedlings did not contain, or show net synthesis of, the 58,000-62,000-mol-wt polypeptide. When dark- grown barley seedlings were illuminated, net synthesis of the apoprotein was observed within the first 15 min of illumination and accumulated apoprotein was measurable after 1 h. After 4 h, P700 chlorophyll a-apoprotein biosynthesis accounted for up to 10% of the total cellular membrane protein synthesis. Changes in the rate of synthesis during chloroplast development suggest coordination between production of the 58,000-62,000-mol-wt polypeptide and the accumulation of chlorophyll. However, when plants were returned to darkness after a period of illumination (4 h) P700 chlorophyll a-apoprotein synthesis continued for a period of hours though at a reduced rate. Thus we found that neither illumination nor the rate of chlorophyll synthesis directly control the rate of apoprotein synthesis. The rapidity of the light-induced change in net synthesis of the apoprotein indicates that this response is tightly coupled to the primary events of light-induced chloroplast development. The data also demonstrate that de novo synthesis of the apoprotein is required for the onset of photosystem I activity in greening seedlings.     

Photosynthetic Membranes of Porphyridium cruentum: An Analysis of Chlorophyll-Protein Complexes and Heme-Binding Proteins

Three chlorophyll-protein complexes (CP I, CP III, CP IV) were electrophoretically separated from thylakoids of the eukaryotic red alga Porphyridium cruentum. CP I contained the primary photochemical reaction center of photosystem I as judged by its light-induced reversible absorbance change at 700 nanometers, by its fluorescence emission maximum at 720 nanometers (−196°C), and by the molecular weight of its apoprotein (68,000 daltons). CP III and CP IV appeared to belong with photosystem II as suggested by the absence of light-reversible absorbance at 700 nanometers, by their fluorescence maximum at 690 nanometers (−196°C), and by the presence of a chlorophyll-binding polypeptide with a molecular weight of about 52,000 daltons. CP IV when completely denatured had two additional polypeptides of about 40,000 and 48,000 daltons. All three chlorophyll-protein complexes contained carotenoids: the chlorophyll/carotenoid molar ratio of 15:1 for CP I, and 20:1 for CP III and CP IV. The thylakoid membranes of P. cruentum contained four cytochromes, detected by heme-dependent peroxidase activity, but there was no observed association with the electrophoretically separated chlorophyll-protein complexes.     

Chlorophyll-Protein Complexes from the Red-Tide Dinoflagellate, Gonyaulax polyedra Stein : Isolation, Characterization, and the Effect of Growth Irradiance on Chlorophyll Distribution

A comparision of high (330 microeinsteins per meter squared per second) and low (80 microeinsteins per meter squared per second) light grown Gonyaulax polyedra indicated a change in the distribution of chlorophyll a, chlorophyll c₂, and peridinin among detergent-soluble chlorophyll-protein complexes. Thylakoid fractions were prepared by sonication and centrifugation. Chlorophyll-protein complexes were solubilized from the membranes with sodium dodecyl sulfate and resolved by Deriphat electrophoresis. Low light cells yielded five distinct chlorophyll-protein complexes (I to V), while only four (I′ to IV′) were evident in preparations of high light cells. Both high molecular weight complexes I and I′ were dominated by chlorophyll a absorption and associated with minor amounts of chlorophyll c. Both complexes II and II′ were chlorophyll a-chlorophyll c₂-protein complexes devoid of peridinin and unique to dinoflagellates. The chlorophyll a:c₂ molar ratio of both complexes was 1:3, indicating significant chlorophyll c enrichment over thylakoid membrane chlorophyll a:c ratios of 1.8 to 2:1. Low light complex III differed from all other high or low light complexes in that it possessed peridinin and had a chlorophyll a:c₂ ratio of 1:1. Low light complexes IV and V and high light complexes III′ and IV′ were spectrally similar, had high chlorophyll a:c₂ ratios (4:1), and were associated with peridinin. The effects of growth irradiance on the composition of chlorophyll-protein complexes in Gonyaulax polyedra differed from those described for other chlorophyll c-containing plant species.     

Light- and MgCl2-dependent characteristics of four chlorophyll-protein complexes isolated from the marine dinoflagellate,Glenodinium sp.

Chlorophyll-protein complexes previously isolated from low-light (80 μE·m⁻²·s⁻¹) log cultures of the marine dinoflagellate, Glenodinium sp., were further characterized. SDS solubilization in combination with polyacrylamide gel electrophoresis in the presence of Deriphat 160-C resolved four discrete chlorophyll-protein bands. In order to elucidate the functional role of Glenodinium sp., room-temperature absorption and fluorescence spectra, protein composition, and pigment molar ratios were obtained for each complex. Results indicated that complex I was analogous to the green plant Photosystem I complex and was also associated with light-harvesting chlorophyll c₂. Complex II was highly enriched in chlorophyll c₂, devoid of peridinin, and demonstrated energy transfer from chlorophyll c to chlorophyll a within the complex, indicating the presence of a light-harvesting component. Based on peridinin: chlorophyll a ratios and fluorescence excitation spectra analyses for complexes III and IV, it was concluded that these complexes contained functional peridinin-chlorophyll a-protein complexes. Changing the ionic environment during isolation of the complexes, or altering the growth irradiance of Glenodinium sp. cultures, resulted in a significant alteration of distribution of chlorophyll a among the chlorophyll-protein complexes.     

Appearance of Chlorophyll-Protein Complexes in Greening Barley Seedlings

The sequential appearance of chlorophyll-protein complexes (CP)in greening barley leaves was studied by an improved methodof SDS-polyacrylamide gel electrophoresis (PAGE). Solubilizedthylakoid membranes were purified using a sucrose step gradientand CPs were separated by PAGE with low concentrations of SDSin solubilizing and reservoir buffers. At 10 min after the onsetof illumination, a chlorophyll-protein complex (CPX) was detected.It was a labile CP, its chlorophyll (Chl) being easily releasedfrom the apoprotein during electrophoresis. The P700-chlorophylla/b-protein complex (CPl) appeared after 45–60 min ofillumination together with P700 activity. Light-harvesting chlorophylla/b-protein complex (LHCP) began to accumulate at 2.5 h withthe beginning of Chl b synthesis. In some cases a small amountof CPa could be detected after 6 h of greening. The time-differencespectrum between homogenates of leaves illuminated for 30 and60 min had an absorbance maximum at 677 nm, showing that a redshift indicative of CPl formation began soon after completionof the Shibata shift. The time-difference spectrum between 3.5-hand 4.0-h illuminated leaves resembled the absolute spectrumof fully greened leaves, indicating that at this stage, spectralcomponents were being synthesized at the same ratio at whichthey exist in fully greened tissues. Both absolute and time-differencespectral data supported the SDS-PAGE results. (Received February 27, 1985; Accepted May 8, 1985)     

Immunocytochemical and Cytochemical Localization of Photosystems I and II

Cytochemical and immunocytochemical methods were used to localize photosystems I and II in barley (Hordeum vulgare L. cv Himalaya) chloroplasts. PSI activity, monitored by diaminobenzidine oxidation, was associated with the lumen side of the thylakoids of both grana and stroma lamellae. The P₇₀₀ chlorophyll a protein, the reaction center of PSI, was localized on thin sections of barley chloroplasts using monospecific antibodies to this protein and the peroxidase-antiperoxidase procedure. Results obtained by immunocytochemistry were similar to those of the diaminobenzidine oxidation: both grana and stroma lamellae contained immunocytochemically reactive material. Both the grana and stroma lamellae were also labeled when isolated thylakoids were reacted with the P₇₀₀ chlorophyll a protein antiserum and then processed by the peroxidase-antiperoxidase procedure. PSII activity was localized cytochemically by monitoring the photoreduction of thiocarbamyl nitroblue tetrazolium, a reaction sensitive to the PSII inhibitor, DCMU. PSII reactions occurred primarily on the grana lamellae, with weaker reactions on the stroma lamellae.     

Polypeptide composition of chlorophyll-protein complexes from romaine lettuce

The protein moiety of the two major chlorophyll-protein complexes associated with chloroplast membranes of outer, dark green leaves of a romaine lettuce shoot (Lactuca sativa L. var. Romana) has been analyzed by discontinuous sodium dodecyl sulfate-polyacrylamide disc gel electrophoresis. Complex II, also termed light-harvesting chlorophyll-protein complex, is shown to consist of a major polypeptide of 25 kilodaltons (kD) and two minor ones of 27.5 and 23 kD. The 25 kD subunit is the single largest polypeptide component of the chloroplast membranes, accounting for about 25% of their total protein. Complex I contains only high molecular weight subunits, the major one being at 67 kD, these subunits representing only a small percentage of the chloroplast membrane total protein.