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.     

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.

     

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.     

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.     

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.     

Morphological, physiological, cytological and phytochemical studies in diploid and colchicine-induced tetraploid plants of Echinacea purpurea (L.)

Echinacea purpurea (L.) is one of the important medicinal plant species. To obtain the tetraploid plants of Echinacea purpurea with improved medicinal qualities, the root tips of two true leaves seedlings were imbibed in 0.25 % (w/v) colchicine solution for 24, 48, 72, 96 and 168 h. The ploidy level of plants was determined by chromosome counting of root tip cells, and confirmed by flow cytometric analysis. Tetraploid induction occurred in seedlings treated for 24, 48 and 72 h at colchicine solution. The morphological, physiological, cytological, and phytochemical characteristics of diploid and colchicine-induced tetraploid plants were compared. Results indicated that tetraploid plants had considerable larger stomata, pollen grain, seed and flower. Moreover, chloroplast number in guard cells, amount of chlorophyll (a, b, and a + b), carotenoids as well as width and thickness of leaves were increased in tetraploids. However, stomata frequency, leaf index, plant height, and quantum efficiency of photosystem II in tetraploid were lower than diploid plants. High-performance liquid chromatography analysis showed that leaves of the tetraploid plants had more cichoric acid (45 %) and chlorogenic acid (71 %) than diploid plants. It was concluded that morphological and physiological characteristics can be used as useful parameters for preliminary screening of putative tetraploids in this species.     

Participation of Chlorophyll b Reductase in the Initial Step of the Degradation of Light-harvesting Chlorophyll a/b-Protein Complexes in Arabidopsis

The light-harvesting chlorophyll a/b-protein complex of photosystem II (LHCII) is the most abundant membrane protein in green plants, and its degradation is a crucial process for the acclimation to high light conditions and for the recovery of nitrogen (N) and carbon (C) during senescence. However, the molecular mechanism of LHCII degradation is largely unknown. Here, we report that chlorophyll b reductase, which catalyzes the first step of chlorophyll b degradation, plays a central role in LHCII degradation. When the genes for chlorophyll b reductases NOL and NYC1 were disrupted in Arabidopsis thaliana, chlorophyll b and LHCII were not degraded during senescence, whereas other pigment complexes completely disappeared. When purified trimeric LHCII was incubated with recombinant chlorophyll b reductase (NOL), expressed in Escherichia coli, the chlorophyll b in LHCII was converted to 7-hydroxymethyl chlorophyll a. Accompanying this conversion, chlorophylls were released from LHCII apoproteins until all the chlorophyll molecules in LHCII dissociated from the complexes. Chlorophyll-depleted LHCII apoproteins did not dissociate into monomeric forms but remained in the trimeric form. Based on these results, we propose the novel hypothesis that chlorophyll b reductase catalyzes the initial step of LHCII degradation, and that trimeric LHCII is a substrate of LHCII degradation.     

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.     

The P700-chlorophyll a-protein. Isolation and some characteristics of the complex in higher plants

A P700-chlorophyll a-protein complex has been purified from several higher plants by hydroxylapatite chromatography of Triton X-100-dissociated chloroplast membranes. The isolated material exhibits a red wavelength maximum at 677 nm, major spectral forms of chlorophyll a at 662, 669, 677, and 686 nm, a chlorophyll/P700 ratio of $\text{40–45}\text{1}$, and contains only chlorophyll a and β-carotene of the photosynthetic pigments present in the chloroplast. The spectral characteristics and composition of the higher plant material are homologous to those of the P700-chlorophyll a-protein previously isolated from blue-green algae; however, unlike the blue-green algal component, cytochromes f and b₆ are associated with the higher plant material. Evidence is presented that a chlorophyll a-protein termed “Complex I” which can be isolated from sodium dodecyl sulfate extracts of chloroplast membranes is a spectrally altered form of the eucaryotic P700-chlorophyll a-protein. The isolation procedure described in this paper is a more rapid technique for obtaining the heart of photosystem I than presently exists; furthermore, the P700 photooxidation and reduction kinetics in the fraction are improved over those in other isolated components showing the same enrichment of P700. It appears very probable that the heart of photosystem I is organized in the same manner in all chlorophyll a-containing organisms.     

Structural and functional relationships in developing Pinus silvestris chloroplasts

The light dependent chloroplast development of dark grown seedlings of Pinus silvestris L. was followed by analyses of chlorophyll content, chlorophyll a/b ratios, chlorophyll/P700 ratios, chlorophyll-protein complexes and structural changes. Low-temperature fluorescence emission spectra of isolated chloroplasts and separation of sodium dodecyl sulphate solubilized chlorophyll-protein complexes by gel electrophoresis showed that the chlorophyll-protein complexes of photosystem 1 (P700-CPa), photosystem II (PS II-CPa) and the light-harvesting complex LH–CPa/b were present in dark grown seedlings. The low-temperature fuoorescence emission maxima of isolated P700–CPa and PS II–CPa shifted towards longer wavelengths during greening in light, indicating a light induced change of the chlorophyll organisation in the two photosystems. Illumination caused LH–CPa/b to increase relative to P700–CPa, whereas the ratio between LH–CPa/b and PS II–CPa remained essentially constant. Analyses of low-temperature fluorescence spectra with or without 0.01 M Mg²⁺ showed that the Mg²⁺ controlled distribution of excitation energy into PS I was activated upon illumination of the seedlings. The photosynthetic unit size, as defined by the chlorophyll/P700 ratio, did not change over a 96 h illumination period, although the chlorophyll content increased about 6–fold during that time. This result and the constant electron transport rate per unit chlorophyll and time during chlorophyll accumulation provided evidence for a sequential development of the photosynthetic units when illuminating dark grown pine cotyledons. Electron micrographs showed that exposure of dark grown seedlings to light for 2 h caused the prolamellar body to disappear and grana to form. These changes occurred prior to substantial accumulation of chlorophyll or change in the ratio between LH–CPa/b and P700–CPa. However, both the water-splitting system of photosystem II and the Mg²⁺ controlled redistribution of excitation energy was activated during this period.     

Ploidy Effects in Isogenic Populations of Alfalfa : II. Photosynthesis, Chloroplast Number, Ribulose-1,5-Bisphosphate Carboxylase, Chlorophyll, and DNA in Protoplasts

Photosynthetically-active protoplasts isolated from isogenic sets of diploid-tetraploid and tetraploid-octoploid alfalfa (Medicago sativa L.) leaves were used to investigate the consequences of polyploidization on several aspects related to photosynthesis at the cellular level. Protoplasts from the tetraploid population contained twice the amount of DNA, ribulose-1,5-bisphosphate carboxylase (RuBPCase), chlorophyll (Chl), and chloroplasts per cell compared to protoplasts from the diploid population. Although protoplasts from the octoploid population contained nearly twice the number of chloroplasts and amount of Chl per cell as tetraploid protoplasts, the amount of DNA and RuBPCase per octoploid cell was only 50% higher than in protoplasts from the tetraploid population. The rate of CO₂-dependent O₂ evolution in protoplasts nearly doubled with an increase in ploidy from the diploid to tetraploid level, but increased only 67% with an increase in ploidy from the tetraploid to octoploid level. Whereas leaves and protoplasts had similar increases in RuBPCase, DNA, and Chl with increase in ploidy level, it was concluded that increased cell volume rather than increased cell number per leaf is responsible for the increase in leaf size with ploidy.     

Relation between the Light-Harvesting Chlorophyll a-Protein Complex LHCPa and Photosystem I in the Alga Chlamydobotrys stellata

The light-harvesting chlorophyll protein system of the alga Chlamydobotrys stellata consists of an as yet uncharacterized algal chlorophyll a-protein, called LHCPa, and a common photosystem II-related chlorophyll a/b-protein, called LHCPb (Brandt, Kaiser-Jarry, Wiessner 1982 Biochim Biophys Acta 679: 404-409). For further characterization, this LHCPa was isolated from the organism by polyacrylamide isoelectrofocusing and reelectrophoresis. It contains only chlorophyll a and has only one apoprotein (32,000 daltons). When separated from autotrophically grown cells, its absorption peak is at 674 nm and its isoelectric point at 5.3. Photoheterotrophic cultivation of the algae shifts the absorption maximum of LHCPa to 679 nm and its isoelectric point to 4.8. This LHCPa is a component of photosystem I particles. In relation to the total chlorophyll a content, the amount of LHCPa is low in autotrophic algae, but increases under photoheterotrophic growth conditions, where the organisms do not have the ability to assimilate CO₂ photosynthetically.     

Biochemical characteristics of thylakoid membranes in chloroplasts of dark-grown pine cotyledons

Japanese black pine (Pinus thunbergii) cotyledons were found to synthesize chlorophylls in complete darkness during germination, although the synthesis was not as great as that in the light. The compositions of thylakoid components in plastids of cotyledons grown in the dark and light were compared using sodium dodecyl sulfate-polyacrylamide gel electrophoresis patterns of polypeptides and spectroscopic determination of membrane redox components. All thylakoid membrane proteins found in preparations from light-grown cotyledons were also present in preparations from dark-grown cotyledons. However, levels of photosystem I, photosystem II, cytochrome b_[ill]/f, and light-harvesting chlorophyll-protein complexes in dark-grown cotyledons were only one-fourth of those in light-grown cotyledons, on a fresh weight basis. These results suggest that the low abundance of thylakoid components in dark-grown cotyledons is associated with the limited supply of chlorophyll needed to assemble the two photosystem complexes and the light-harvesting chlorophyll-protein complex.     

Chloroplast composition and structure differences in a soybean mutant

A nuclear mutation of Glycine max (soybean) segregates 1:2:1 in regard to chlorophyll content. The heterozygous (LG) leaf blade contains about one-half the pigment content of the wild type (DG) per gram fresh weight. A lethal yellow (LY) type contains about 1 to 2% of the DG leaf pigment values. The chlorophyll a/b ratio in the LG is about 5 compared to about 2 in the DG. Protein/leaf values are lower in the LG and LY types when compared to DG. The LG plastid lamellae contain more protein/chlorophyll, cytochromes/chlorophyll, and quinones/chlorophyll than the DG. P₇₀₀/chlorophyll values are similar in the DG and LG types.     

The Light-harvesting Chlorophyll a/b-Protein Complex of Chlamydomonas reinhardii

The molecular organization of chlorophyll in Chlamydomonas reinhardii has been shown to be essentially similar to that in higher plants. Some 50% of the chlorophyll in Chlamydomonas reinhardii chloroplast membranes has been shown to be located in a chlorophyll a/b-protein complex. The complex was isolated in a homogeneous form by hydroxylapatite chromatography of sodium dodecyl sulfate extracts of the chloroplast membranes. Its absorption spectrum exhibits two maxima in the red region at 670 and 652 nm due to the presence of equimolar quantities of chlorophylls a and b in the complex. Preparations of the chlorophyll-protein also contain some of each of the carotenoids observed in the intact chloroplast membrane, but not in the same proportions. The native complex (S value = 2.3S) exhibits a molecular weight of 28,000 ± 2,000 on calibrated sodium dodecyl sulfate-polyacrylamide gel electrophoresis. However, on the basis of its amino acid composition and other data a more probable molecular weight of about 35,000 was calculated. Each 35,000 dalton unit contains three chlorophyll a and three chlorophyll b molecules, and on the average one carotenoid molecule conjugated with probably a single polypeptide of 29,000 daltons. Comparison of spectral and biochemical characteristics demonstrates that this algal chlorophyll-protein is homologous to the previously described major light-harvesting chlorophyll a/b-protein of higher plants. It is anticipated that the Chlamydomonas complex functions solely in a light-harvesting capacity in analogy to the function determined for the higher plant component.     

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; )     

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.     

Seasonal Effects on Chlorophyll-Protein Complexes Isolated from P-inus silvestris

The seasonal changes in the relative distribution of P700 chlorophyll-protein complex a₁ and light harvesting chlorophyll-protein complex a/b were studied in a natural stand of Pinus silvestris. Similar measurements were made after artificial photobleaching of chlorophyll in pine seedlings or in isolated pine chloroplasts. The chlorophyll-protein complexes were solubilized by sodium dodecyl sulphate and separated by polyacrylamide gel electrophoresis. When autumn and winter destruction of chlorophyll occurs, the chlorophyll a antenna associated with P700 in photosystem 1 (P700-CPa₁) is relatively more affected than the light harvesting complex, which lacks a reaction centre. These results are further supported by low-temperature fluorescence emission properties of isolated chloroplasts presented in this work and elsewhere. The destruction of chlorophyll in stressing autumn and winter climates is most probably caused by photosensitized oxidation of chlorophyll.     

P(700) Chlorophyll a-Protein : Purification, Characterization, and Antibody Preparation

The P₇₀₀ chlorophyll α-protein was purified by preparative sodium dodecyl sulfate (SDS) gel electrophoresis from SDS-solubilized barley (Hordeum vulgare L., cv Himalaya) chloroplast membranes. After elution from the gel in the presence of 0.05 to 0.1% Triton X-100, the recovered protein had a chlorophyll/P₇₀₀ ratio of 50 to 60/1 and contained no chlorophyll b or cytochromes. Analysis of the polypeptide composition of the chlorophyll-protein revealed a 58 to 62 kilodalton (kD) polypeptide component but no lower molecular weight polypeptides. The 58 to 62 kD component was further resolved into two distinct polypeptide bands which were subsequently mapped by partial cyanogen bromide digestion and Staphylococcus aureus proteolysis. Based on results from the mapping experiments and other data, we suggest that the two components are conformational variants of a single polypeptide. Measurement of the chlorophyll to protein ratio by quantitative amino acid analysis and consideration of the yield of P₇₀₀ in the protein isolate suggest that, contrary to previous models (Bengis and Nelson, 1975, 1977), P₇₀₀in vivo is associated with a minimum of four subunits of approximately 60 kD.

Antibodies raised against the photochemically active chlorophyll-protein complex from barley reacted specifically with the 58 to 62 kD apoprotein. The same preparative electrophoresis procedure was used to isolate photochemically active P₇₀₀ chlorophyll a-protein from soybean (Glycine max L.), tobacco (Nicotiana tobacum L.), petunia (Petunia × hybrida), tomato (Lycopersicum esculentum), and Chlamydomonas reinhardti. The isolated complex from all species exhibited identical polypeptide compositions and chlorophyll/P₇₀₀ ratios. Antibodies to the barley protein cross reacted with all species tested demonstrating the highly conserved structure of the apoprotein.