Universal chlorophyll equations for estimating chlorophylls <Emphasis Type="Italic">a,b, c</Emphasis>, and <Emphasis Type="Italic">d</Emphasis> and total chlorophylls in natural assemblages of photosynthetic organisms using acetone,methanol, or ethanol solvents

A universal set of equations for determining chlorophyll (Chl) a, accessory Chl b, c, and d, and total Chl have been developed for 90 % acetone, 100 % methanol, and ethanol solvents suitable for estimating Chl in extracts from natural assemblages of algae. The presence of phaeophytin (Ph) a not only interferes with estimates of Chl a but also with Chl b and c determinations. The universal algorithms can hence be misleading if used on natural collections containing large amounts of Ph. The methanol algorithms are severely affected by the presence of Ph and so are not recommended. The algorithms were tested on representative mixtures of Chls prepared from extracts of algae with known Chl composition. The limits of detection (and inherent error, ±95 % confidence limit) for all the Chl equations were less than 0.03 g m⁻³. The algorithms are both accurate and precise for Chl a and d but less accurate for Chl b and c. With caution the algorithms can be used to calculate a Chl profile of natural assemblages of algae. The relative error of measurements of Chls increases hyperbolically in diluted extracts. For safety reasons, efficient extraction of Chls and the convenience of being able to use polystyrene cuvettes, the algorithms for ethanol are recommended for routine assays of Chls in natural assemblages of aquatic plants.     

Reconstitution of the Peridinin–chlorophyll a Protein (PCP): Evidence for Functional Flexibility in Chlorophyll Binding

The coding regions for the N-domain, and full length peridinin–chlorophyll a apoprotein (full length PCP), were expressed in Escherichia coli. The apoproteins formed inclusion bodies from which the peptides could be released by hot buffer. Both the above constructs were reconstituted by addition of a total pigment extract from native PCP. After purification by ion exchange chromatography, the absorbance, fluorescence excitation and CD spectra resembled those of the native PCP. Energy transfer from peridinin to Chl a was restored and a specific fluorescence activity calculated which was ~86% of that of native PCP. Size exclusion analysis and CD spectra showed that the N-domain PCP dimerized on reconstitution. Chl a could be replaced by Chl b, 3-acetyl Chl a, Chl d and Bchl using the N-domain apo protein. The specific fluorescence activity was the same for constructs with Chl a, 3-acetyl Chl a, and Chl d but significantly reduced for those made with Chl b. Reconstitutions with mixtures of chlorophylls were also made with eg Chl b and Chl d and energy transfer from the higher energy Qy band to the lower was demonstrated.     

Chlorophylls <Emphasis Type="Italic">d</Emphasis> and <Emphasis Type="Italic">f</Emphasis> and their role in primary photosynthetic processes of cyanobacteria

The finding of unique Chl d- and Chl f-containing cyanobacteria in the last decade was a discovery in the area of biology of oxygenic photosynthetic organisms. Chl b, Chl c, and Chl f are considered to be accessory pigments found in antennae systems of photosynthetic organisms. They absorb energy and transfer it to the photosynthetic reaction center (RC), but do not participate in electron transport by the photosynthetic electron transport chain. However, Chl d as well as Chl a can operate not only in the light-harvesting complex, but also in the photosynthetic RC. The long-wavelength (Q_y) Chl d and Chl f absorption band is shifted to longer wavelength (to 750 nm) compared to Chl a, which suggests the possibility for oxygenic photosynthesis in this spectral range. Such expansion of the photosynthetically active light range is important for the survival of cyanobacteria when the intensity of light not exceeding 700 nm is attenuated due to absorption by Chl a and other pigments. At the same time, energy storage efficiency in photosystem 2 for cyanobacteria containing Chl d and Chl f is not lower than that of cyanobacteria containing Chl a. Despite great interest in these unique chlorophylls, many questions related to functioning of such pigments in primary photosynthetic processes are still not elucidated. This review describes the latest advances in the field of Chl d and Chl f research and their role in primary photosynthetic processes of cyanobacteria.     

An overview on chlorophylls and quinones in the photosystem I-type reaction centers

Minor but key chlorophylls (Chls) and quinones in photosystem (PS) I-type reaction centers (RCs) are overviewed in regard to their molecular structures. In the PS I-type RCs, the prime-type chlorophylls, namely, bacteriochlorophyll (BChl) a′ in green sulfur bacteria, BChl g′ in heliobacteria, Chl a′ in Chl a-type PS I, and Chl d′ in Chl d-type PS I, function as the special pairs, either as homodimers, (BChl a′)₂ and (BChl g′)₂ in anoxygenic organisms, or heterodimers, Chl a/a′ and Chl d/d′ in oxygenic photosynthesis. Conversions of BChl g to Chl a and Chl a to Chl d take place spontaneously under mild condition in vitro. The primary electron acceptors, A ₀, are Chl a-derivatives even in anoxygenic PS I-type RCs. The secondary electron acceptors are naphthoquinones, whereas the side chains may have been modified after the birth of cyanobacteria, leading to succession from menaquinone to phylloquinone in oxygenic PS I.     

Photosystem 2-activity and thylakoid membrane polypeptides of <Emphasis Type="Italic">in vitro</Emphasis> cultured chrysanthemum as affected by NaCl

Long-term (30 d) effects of 100, 200, 300, and 400 mM NaCl on photosystem 2 (PS 2)-mediated electron transport activity and content of D1 protein in the thylakoid membranes of chrysanthemum (Dendranthema grandiflorum) cultured in vitro at low irradiance 20 μmol(photon) m⁻² s⁻¹ were investigated. 100 mM NaCl increased contents of chlorophylls (Chl) a and b, carotenoids (Car; xanthophylls + carotenes), and the ratio of Chl a/b, and Car/Chl a+b. However, further increase in NaCl concentration led to the significant reduction in the contents of Chl a, and Chl b, and increase in the ratio of Chl a/b and Car/Chl a+b. NaCl treatment decreased the PS 2-mediated electron transport activity and contents of various thylakoid membrane polypeptides including D1 protein.     

Excitation relaxation dynamics and energy transfer in fucoxanthin–chlorophyll a/c-protein complexes,probed by time-resolved fluorescence

In algae, light-harvesting complexes contain specific chlorophylls (Chls) and keto-carotenoids; Chl a, Chl c, and fucoxanthin (Fx) in diatoms and brown algae; Chl a, Chl c, and peridinin in photosynthetic dinoflagellates; and Chl a, Chl b, and siphonaxanthin in green algae. The Fx–Chl a/c-protein (FCP) complex from the diatom Chaetoceros gracilis contains Chl c₁, Chl c₂, and the keto-carotenoid, Fx, as antenna pigments, in addition to Chl a. In the present study, we investigated energy transfer in the FCP complex associated with photosystem II (FCPII) of C. gracilis. For these investigations, we analyzed time-resolved fluorescence spectra, fluorescence rise and decay curves, and time-resolved fluorescence anisotropy data. Chl a exhibited different energy forms with fluorescence peaks ranging from 677 nm to 688 nm. Fx transferred excitation energy to lower-energy Chl a with a time constant of 300 fs. Chl c transferred excitation energy to Chl a with time constants of 500–600 fs (intra-complex transfer), 600–700 fs (intra-complex transfer), and 4–6 ps (inter-complex transfer). The latter process made a greater contribution to total Chl c-to-Chl a transfer in intact cells of C. gracilis than in the isolated FCPII complexes. The lower-energy Chl a received excitation energy from Fx and transferred the energy to higher-energy Chl a. This article is part of a Special Issue entitled: Photosynthesis Research for Sustainability: Keys to Produce Clean Energy.     

Interconversions of Chlorophylls a and b Synthesized from Exogenous Chlorophyllides a and b in Etiolated and Post-Etiolated Rye Seedlings

A comparative study of reciprocal conversions of chlorophylls a and b (Chl aand Chl b) in etiolated and post-etiolated rye seedlings (Secale cereale L.) was performed. The production of these pigments was initiated by infiltration of exogenous chlorophyllides a and b (Chlide a and b). It was shown that Chlide b, when infiltrated into etiolated rye seedlings, was esterified, producing Chl b. A major portion of Chl b (more than 80%) was transformed into Chl aduring long-term seedling dark exposure. The high rate of Chl b conversion into Chl a in the pool of pigments of exogenous origin was also observed during the lag-phase when there was no chlorophyll formation from endogenous precursors. The infiltration of Chlide a resulted in Chl a formation. The efficiency of its conversion into Chl b was low (about 1%) in the etiolated seedlings but increased during their greening. In the post-etiolated seedlings infiltrated with Chlide b, which were preliminary illuminated for 6–12 h, the Chl /Chl a ratio was almost similar in the pools of pigments synthesized from both exogenous and endogenous precursors. The rates of direct and reverse reactions responsible for the interconversion of Chl aand Chl b depended on the stage of the formation of the photosynthetic apparatus during greening of etiolated seedlings, when the particular structural components are formed in a definite sequence.     

Optical properties and optical constituents of the Faroe Islands shelf and off-shelf waters,North East Atlantic

The study comprises a data set of CTD, optical properties—K ₀(PAR), c _p, a(PAR), b(PAR)—and optical constituents—Chl a, SPM, CDOM—from 72 shelf and off-shelf stations in the Faroe Islands (62°N, 7°W) North East Atlantic, in early spring 2005. Results showed that shelf waters surrounding the islands were cold and low saline, whereas off-shelf waters were warmer (~1°C) and more saline (~0.05) PSU. A pronounced oceanographic front separated the two waters, and diffuse light attenuation K ₀(PAR), beam attenuation c _p, Chl a, absorption a(PAR), and scattering coefficient b(PAR) were all significantly higher on the shelf. Analyses showed that off-shelf light attenuation K ₀(PAR) was governed by Chl a, shown by a high (r ² = 0.64) Chl a–K ₀(PAR) correlation, whereas light attenuation on the shelf was governed by both Chl a, SPM, and CDOM in combination. A Chl a specific diffuse attenuation coefficient K₀^* ( \textPAR ) K_{0}^{*} \left( {\text{PAR}} \right) of 0.056 (m² mg⁻¹ Chl a) and a Chl a specific beam attenuation ( c_\textp^* c_{\text{p}}^{*} ) of 0.27 (m² mg⁻¹ Chl a) coefficients were derived for the off-shelf. It is pointed out that Chl a is the single variable that changes over time as no rivers with high SPM and CDOM enter the shelf area. Data were obtained in early spring, and Chl a concentrations were low ~0.5 mg Chl a m⁻³. Spring bloom Chl a are about 10 mg Chl a m⁻³ and estimations showed that shelf K ₀(PAR) will increase about 5 times and beam attenuation about 10 times. The Faroe Islands shelf–off-shelf waters is a clear example where physical conditions maintain some clear differences in optical properties and optical constituents. The complete data set is enclosed.     

Singlet and triplet excited state properties of natural chlorophylls and bacteriochlorophylls

Ten naturally occurring chlorophylls (a, b, c ₂, d) and bacteriochlorophylls (a, b, c, d, e, g) were purified and studied using the optical spectroscopic techniques of both steady state and time-resolved absorption and fluorescence. The studies were carried out at room temperature in nucleophilic solvents in which the central Mg is hexacoordinated. The comprehensive studies of singlet excited state lifetimes show a clear dependency on the structural features of the macrocycle and terminal substituents. The wide-ranging studies of triplet state lifetime demonstrate the existence of an energy gap law for these molecules. The knowledge of the dynamics and the energies of the triplet state that were obtained in other studies allowed us to construct an energy gap law expression that can be used to estimate the triplet state energies of any (B)chlorophyll molecule from its triplet lifetime obtained in a liquid environment.     

Chlorophyll fluorescence imaging of photosynthetic activity in sun and shade leaves of trees

The differences in pigment levels, photosynthetic activity and the chlorophyll fluorescence decrease ratio R _Fd (as indicator of photosynthetic rates) of green sun and shade leaves of three broadleaf trees (Platanus acerifolia Willd., Populus alba L., Tilia cordata Mill.) were compared. Sun leaves were characterized by higher levels of total chlorophylls a + b and total carotenoids x + c as well as higher values for the weight ratio chlorophyll (Chl) a/b (sun leaves 3.23–3.45; shade leaves: 2.74–2.81), and lower values for the ratio chlorophylls to carotenoids (a + b)/(x + c) (with 4.44–4.70 in sun leaves and 5.04–5.72 in shade leaves). Sun leaves exhibited higher photosynthetic rates P _N on a leaf area basis (mean of 9.1–10.1 μmol CO₂ m⁻² s⁻¹) and Chl basis, which correlated well with the higher values of stomatal conductance G _s (range 105–180 mmol m⁻² s⁻¹), as compared to shade leaves (G _s range 25–77 mmol m⁻² s⁻¹; P _N: 3.2–3.7 μmol CO₂ m⁻² s⁻¹). The higher photosynthetic rates could also be detected via imaging the Chl fluorescence decrease ratio R _Fd, which possessed higher values in sun leaves (2.8–3.0) as compared to shade leaves (1.4–1.8). In addition, via R _Fd images it was shown that the photosynthetic activity of the leaves of all trees exhibits a large heterogeneity across the leaf area, and in general to a higher extent in sun leaves than in shade leaves.     

Pigment exchange of Photosystem II reaction center by chlorophyll d

Pigment exchanges among photosystem reaction centers (RCs) are useful for the identification and functional analysis of chromophores in photosynthetic organisms. Pigment replacement within the spinach Photosystem II RC was performed with Chl d derived from the oxygenic alga Acaryochloris marina, using a protocol similar to that reported previously [Gall et al. (1998) FEBS Lett 434: 88–92] based on the incubation of reaction centers with an excess of other pigments. In this study, we analyzed Chl d-modified monomeric RC which was separated from Chl d-modified dimeric RC by size-exclusion chromatography. Based on the assumption of a constant ratio of two Pheo a molecules per RC, the number of Chl a molecules in Chl d-modified monomeric RCs was found to decrease from six to four. The absorption spectrum of the Chl d-modified monomeric RC at room temperature showed a large peak at 699.5 nm originating from Chl d and a small peak at 672.5 nm orignating from Chl a. Photoaccumulation of the Pheo a⁻ in Chl d-modified monomeric RC, in the presence of sodium dithionate and methyl viologen, did not differ significantly from that in control RC, showing that the Chl d-modified monomeric RC retains its charge separation activity and photochemically active Pheo a.     

Structural-functional organization of the main light harvesting complex and photosystem 2 of higher plants

The interrelation between spectral and structural–functional properties of LhcIIb was studied. The dipole strength of the main Q_y bands of chlorophylls (Chl a 30.8 D²; Chl b 18.5 D²) and chlorophyll a/b ratio (Chl a/Chl b = 7 : 6) were determined for LhcIIb. The Chl a/Chl b value shows that the subunit of this complex contains seven Chl a and six Chl b molecules. Individual bands of chlorophylls (bands in stokes and anti-Stokes parts at 77 K were Lorentzian and Gaussian, respectively) were resolved using synchronized deconvolution of absorption, CD, and LD bands of chlorophylls. Seven of these bands belonged to Chl a. Parameters of absorption bands of Chl a indicate that seven molecules represent a united cluster (heptamer) with exciton interactions, determining the spectrum of LhcIIb in the Chl a absorption region. Parameters of absorption bands of Chl b show the existence of three clusters: monomer (639.6 nm), dimer (645.2 and 647.4 nm), and trimer (649.8 and 654.1 nm). These clusters and their properties agree with the well-known structure of porphyrin groups of the LhcIIb subunit (Kuhlbrandt, 1994). A distorted ring of seven porphyrins in the stromal range of the subunit corresponds to Chl a heptamer; a separately located molecule near the N-terminal domain on the stromal side of the subunit corresponds to Chl b monomer; a dimer and a trimer of porphyrins in the lumenal range of the subunit correspond to the dimer and trimer of Chl b, respectively. The calculated lifetimes of the excitation energy (exciton) transfer in subunit and trimer of LhcIIb confirm this location of pigments. The geometry of the Chl a heptamer (mutual orientation of transition dipole moments) was determined by the steady-state Kasha–Tinoco approximation using parameters of individual bands of exciton splitting. The calculated parameters of mutual orientation of Chl a dipoles agree with the topography of the stromal porphyrins found by electron crystallography (Kuhlbrandt, 1994). A structural model of the granal multicentral macrocomplex of PSII (MPSII) is suggested. The lifetimes of the exciton migration between the main pigment–protein compartments of MPSII were calculated. The results of calculation are consistent with the structural model of the photosystem. The location of pigments provides for fast exciton hopping between Chl a clusters of neighboring proteins in the MPSII along the stromal surface within the membrane (5-25 psec) and between stacked membranes (40 psec) of chloroplast grana.     

Photosynthesis performance in sweet almond [<Emphasis Type="Italic">Prunus dulcis</Emphasis> (Mill) D. Webb] exposed to supplemental UV-B radiation

Due to anthropogenic influences, solar UV-B irradiance at the earth’s surface is increasing. To determine the effects of enhanced UV-B radiation on photosynthetic characteristics of Prunus dulcis, two-year-old seedlings of the species were submitted to four levels of UV-B stress, namely 0 (UV-B_c), 4.42 (UV-B₁), 7.32 (UV-B₂) and 9.36 (UV-B₃) kJ m⁻² d⁻¹. Effects of UV-B stress on a range of chlorophyll (Chl) fluorescence parameters (FPs), Chl contents and photosynthetic gas-exchange parameters were investigated. UV-B stress promoted an increase in minimal fluorescence of dark-adapted state (F₀) and F₀/F_m, and a decrease in variable fluorescence (F_v, F_v/F_m, F_v/F₀ and F₀/F_m) due to its adverse effects on photosystem II (PSII) activity. No significant change was observed for maximal fluorescence of dark-adapted state (F_m). Enhanced UV-B radiation caused a significant inhibition of net photosynthetic rate (P _N) at UV-B₂ and UV-B₃ levels and this was accompanied by a reduction in stomatal conductance (g _s) and transpiration rate (E). The contents of Chl a, b, and total Chl content (a+b) were also significantly reduced at increased UV-B stress. In general, adverse UV-B effects became significant at the highest tested radiation dose 9.36 kJ m⁻² d⁻¹. The most sensitive indicators for UV-B stress were F_v/F₀, Chl a content and P _N. Significant P<0.05 alteration in these parameters was found indicating the drastic effect of UV-B radiation on P. dulcis.     

Intensity of nitrification in soil as a function of time and soil moisture

Proceeding from three previously derived expressions for the intensity of nitrification in soil as a function of time (logΣN=K.logt+q), as a function of incubation moisture (logΣN=A.pF _i+B), as a function of initial moisture (logΣN=C.pF _v+D), it was shown that the nitrification intensity as a function of time and of moisture can be expressed by the bilinear function log ΣN=a.pF _i.logT+b.pF _i+c.logt+d; as a function of time and of initial moisture by the bilinear function logΣ=N=a.pF _v.logt+b.pF _v+c.logt+d; as a function of initial and incubation moisture by the bilinear function log ΣN=a.pF _ipF _v+b.pF _i+c.pF _v+d. The intensity of nitrification as a function of time, incubation moisture and initial moisture may be expressed by the multilinear function log ΣN=a.pF _i.pF _v.logt+b.pF _i.pF _v+c.pF _i.logt+d.pF _v.logt+e .pF _i+f.pF _v=g.logt+h. This function is valid for all the incubation moistures lying between pF _i 3.0 and 4.0 and for all initial moistures between 3.5 and 5.9 provided that the incubation temperature remains constant.     

Sedimentation of chlorophylls in an Arctic fjord under freshwater discharge

Sedimentation of chlorophylls was studied during summer 1997 in Adventfjorden (Spitsbergen, Arctic). During the period of study, the water column was found to be well stratified by a freshened surface layer (salinity <31 PSS). A high load of suspended particulate matter from riverine discharge reduced the euphotic zone to an interval of 0.4–1.1m. Total particulate matter sedimentation rates were about twice as high in June as in July. The following chlorophylls were distinguished in the sedimented particles: chl a and its degradation products (allomer chl a, phaeophytin a, phaeophorbide a, chlorophyllide a), chl b and chl c ₁+c ₂. The quantitatively most important derivative of chl a was phaeophorbide a (31--41% of porphyrin a). Generally, the sedimentation rate of chlorophylls increased with depth. Linear relationships between concentrations of chl a and phaeophorbide a (r ²=0.92), as well as between concentrations of chl a and phaeophytin a (r ²=0.90) indicated a strong connection between phytoplankton abundance and zooplankton grazing. The significant correlation between chl a and chlorophyllide a concentrations (r ²=0.82) showed that most of the sinking chl a belonged primarily to diatoms, and low chlorophyllide a:chl a ratio (0.03) indicated that cellular senescence was not an important reason for the sinking of chl a. Moreover, very low chl b:chl a ratios (about 0.05 calculated for samples where chl b was detectable) suggest that contributions of green algae and/or higher plant detritus were negligible in sinking particles. The ratio of chl c ₁+c ₂:chl a was 0.85 indicating that chl c-containing algae were dominating.     

Optical spectroscopic studies of light-harvesting by pigment-reconstituted peridinin-chlorophyll-proteins at cryogenic temperatures

Low temperature, steady-state, optical spectroscopic methods were used to study the spectral features of peridinin-chlorophyll-protein (PCP) complexes in which recombinant apoprotein has been refolded in the presence of peridinin and either chlorophyll a (Chl a), chlorophyll b (Chl b), chlorophyll d (Chl d), 3-acetyl-chlorophyll a (3-acetyl-Chl a) or bacteriochlorophyll a (BChl a). Absorption spectra taken at 10 K provide better resolution of the spectroscopic bands than seen at room temperature and reveal specific pigment–protein interactions responsible for the positions of the Q_y bands of the chlorophylls. The study reveals that the functional groups attached to Ring I of the two protein-bound chlorophylls modulate the Q_y and Soret transition energies. Fluorescence excitation spectra were used to compute energy transfer efficiencies of the various complexes at room temperature and these were correlated with previously reported ultrafast, time-resolved optical spectroscopic dynamics data. The results illustrate the robust nature and value of the PCP complex, which maintains a high efficiency of antenna function even in the presence of non-native chlorophyll species, as an effective tool for elucidating the molecular details of photosynthetic light-harvesting.     

Lability of chlorophylls in solvent

Journal of Applied Phycology - DMSO (dimethyl sulfoxide, (CH3)2SO) is an alternative solvent for the spectroscopic assay of chlorophylls (Chl) but has mainly been used on Chl a and b organisms, but...     

18O Labeling of Chlorophyll d in Acaryochloris marina Reveals That Chlorophyll a and Molecular Oxygen Are Precursors

The cyanobacterium Acaryochloris marina was cultured in the presence of either H₂¹⁸O or ¹⁸O₂, and the newly synthesized chlorophylls (Chl a and Chl d) were isolated using high performance liquid chromatography and analyzed by mass spectroscopy. In the presence of H₂¹⁸O, newly synthesized Chl a and d, both incorporated up to four isotopic ¹⁸O atoms. Time course H₂¹⁸O labeling experiments showed incorporation of isotopic ¹⁸O atoms originating from H₂¹⁸O into Chl a, with over 90% of Chl a ¹⁸O-labeled at 48 h. The incorporation of isotopic ¹⁸O atoms into Chl d upon incubation in H₂¹⁸O was slower compared with Chl a with ∼50% ¹⁸O-labeled Chl d at 115 h. The rapid turnover of newly synthesized Chl a suggested that Chl a is the direct biosynthetic precursor of Chl d. In the presence of ¹⁸O₂ gas, one isotopic ¹⁸O atom was incorporated into Chl a with approximately the same kinetic incorporation rate observed in the H₂¹⁸O labeling experiment, reaching over 90% labeling intensity at 48 h. The incorporation of two isotopic ¹⁸O atoms derived from molecular oxygen (¹⁸O₂) was observed in the extracted Chl d, and the percentage of double isotopic ¹⁸O-labeled Chl d increased in parallel with the decrease of non-isotopic-labeled Chl d. This clearly indicated that the oxygen atom in the C3¹-formyl group of Chl d is derived from dioxygen via an oxygenase-type reaction mechanism.     

Relative binding affinities of chlorophylls in peridinin–chlorophyll–protein reconstituted with heterochlorophyllous mixtures

Peridinin–chlorophyll–protein (PCP), containing differently absorbing chlorophyll derivatives, are good models with which to study energy transfer among monomeric chlorophylls (Chls) by both bulk and single-molecule spectroscopy. They can be obtained by reconstituting the N-terminal domain of the protein (N-PCP) with peridinin and chlorophyll mixtures. Upon dimerization of these “half-mers”, homo- and heterochlorophyllous complexes are generated, that correspond structurally to monomeric protomers of native PCP from Amphidinium carterae. Heterochlorophyllous complexes contain two different Chls in the two halves of the complete structure. Here, we report reconstitution of N-PCP with binary mixtures of Chl a, Chl b, and [3-acetyl]-Chl a. The ratios of the pigments were varied in the reconstitution mixture, and relative binding constants were determined from quantification of these pigments in the reconstituted PCPs. We find higher affinities for both Chl b and [3-acetyl]-Chl a than for the native pigment, Chl a.