The Experts below are selected from a list of 255 Experts worldwide ranked by ideXlab platform
Min Chen - One of the best experts on this subject based on the ideXlab platform.
-
In vitro Conversion of Vinyl to Formyl Groups in Naturally Occurring Chlorophylls
Scientific Reports, 2014Co-Authors: Patrick C. Loughlin, Robert D. Willows, Min ChenAbstract:The chemical structural differences distinguishing Chlorophylls in oxygenic photosynthetic organisms are either formyl substitution (Chlorophyll b , d and f ) or the degree of unsaturation (8-vinyl Chlorophyll a and b ) of a side chain of the macrocycle compared with Chlorophyll a . We conducted an investigation of the conversion of vinyl to formyl groups among naturally occurring Chlorophylls. We demonstrated the in vitro oxidative cleavage of vinyl side groups to yield formyl groups through the aid of a thiol-containing compound in aqueous reaction mixture at room temperature. Heme is required as a catalyst in aqueous solution but is not required in methanolic reaction mixture. The conversion of vinyl- to formyl- groups is independent of their position on the macrocycle, as we observed oxidative cleavages of both 3-vinyl and 8-vinyl side chains to yield formyl groups. Three new Chlorophyll derivatives were synthesised using 8-vinyl Chlorophyll a as substrate: 8-vinyl Chlorophyll d , [8-formyl]-Chlorophyll a and [3,8-diformyl]-Chlorophyll a . The structural and spectral properties will provide a signature that may aid in identification of the novel Chlorophyll derivatives in natural systems. The ease of conversion of vinyl- to formyl- in Chlorophylls demonstrated here has implications regarding the biosynthetic mechanism of Chlorophyll d in vivo .
-
extinction coefficient for red shifted Chlorophylls Chlorophyll d and Chlorophyll f
Biochimica et Biophysica Acta, 2012Co-Authors: Nicholas Scales, Robert E. Blankenship, Robert D. Willows, Min ChenAbstract:Abstract Both Chlorophyll f and Chlorophyll d are red-shifted Chlorophylls in oxygenic photosynthetic organisms, which extend photon absorbance into the near infrared region. This expands the range of light that can be used to drive photosynthesis. Quantitative determination of Chlorophylls is a crucial step in the investigation of Chlorophyll-photosynthetic reactions in the field of photobiology and photochemistry. No methods have yet been worked out for the quantitative determination of Chlorophyll f . There is also no method available for the precise quantitative determination of Chlorophyll d although it was discovered in 1943. In order to obtain the extinction coefficients (e) of Chlorophyll f and Chlorophyll d , the concentrations of Chlorophylls were determined by Inductive Coupled Plasma Mass Spectrometry according to the fact that each Chlorophyll molecule contains one magnesium (Mg) atom. Molar extinction coefficient e chl f is 71.11 × 10 3 L mol − 1 A 707 nm cm − 1 and e chl d is 63.68 × 10 3 L mol − 1 A 697 nm cm − 1 in 100% methanol. This article is part of a Special Issue entitled: Photosynthesis Research for Sustainability: from Natural to Artificial.
-
expanding the solar spectrum used by photosynthesis
Trends in Plant Science, 2011Co-Authors: Min Chen, Robert E. BlankenshipAbstract:A limiting factor for photosynthetic organisms is their light-harvesting efficiency, that is the efficiency of their conversion of light energy to chemical energy. Small modifications or variations of Chlorophylls allow photosynthetic organisms to harvest sunlight at different wavelengths. Oxygenic photosynthetic organisms usually utilize only the visible portion of the solar spectrum. The cyanobacterium Acaryochloris marina carries out oxygenic photosynthesis but contains mostly Chlorophyll d and only traces of Chlorophyll a. Chlorophyll d provides a potential selective advantage because it enables Acaryochloris to use infrared light (700–750nm) that is not absorbed by Chlorophyll a. Recently, an even more red-shifted Chlorophyll termed Chlorophyll f has been reported. Here, we discuss using modified Chlorophylls to extend the spectral region of light that drives photosynthetic organisms.
-
a red shifted Chlorophyll
Science, 2010Co-Authors: Min Chen, Hugo Scheer, Robert D. Willows, Martin Schliep, Zheng Li Cai, Brett A NeilanAbstract:Chlorophylls are essential for light-harvesting and energy transduction in photosynthesis. Four chemically distinct varieties have been known for the past 60 years. Here we report isolation of a fifth, which we designate Chlorophyll f. Its in vitro absorption (706 nanometers) and fluorescence (722 nanometers) maxima are red-shifted compared to all other Chlorophylls from oxygenic phototrophs. On the basis of the optical, mass, and nuclear magnetic resonance spectra, we propose that Chlorophyll f is [2-formyl]-Chlorophyll a (C 55 H 70 O 6 N 4 Mg). This finding suggests that oxygenic photosynthesis can be extended further into the infrared region and may open associated bioenergy applications.
-
Nomenclature for membrane-bound light-harvesting complexes of cyanobacteria
Photosynthesis Research, 2008Co-Authors: Min Chen, Yinan Zhang, Robert E. BlankenshipAbstract:Accessory Chlorophyll-binding proteins (CBP) in cyanobacteria have six transmembrane helices and about 11 conserved His residues that might participate in Chlorophyll binding. In various species of cyanobacteria, the CBP proteins bind different types of Chlorophylls, including Chlorophylls a, b, d and divinyl-Chlorophyll a, b . The CBP proteins do not belong to the light-harvesting complexes (LHC) superfamily of plant and algae. The proposed new name of CBP for this class of proteins, which is a unique accessory light-harvesting superfamily in cyanobacteria, clarifies the confusion of names of prochlorophytes Chlorophyll binding protein (Pcb), PSII-like light-harvesting proteins and iron-stress-induced protein A (IsiA). The CBP complexes are a member of a larger family that includes the Chlorophyll a -binding proteins CP43 and CP47 that function as core antennas of photosystem II.
Rafael Picorel - One of the best experts on this subject based on the ideXlab platform.
-
pigment content of d1 d2 cytochrome b559 reaction center preparations after removal of cp47 contamination an immunological study
Biochemistry, 1995Co-Authors: Jose Javier Pueyo, Michael Seibert, Esmeralda Moliner, Rafael PicorelAbstract:Isolated D1 -D2-cytochrome b559 photosystem I1 reaction center preparations with pigment stoichiometry higher than 4 Chlorophylls per 2 pheophytins can be contaminated with CP47 proximal antenna complex. Reaction centers prepared by a modification of the Nanba-Satoh procedure and containing about 6 Chlorophylls per 2 pheophytins showed immuno-cross-reactivity when probed with a monoclonal antibody raised against the CP47 polypeptide. Furthermore, they could be fractionated successfully by Superose- 12 sieve chromatography into two different populations. The first few fractions off the column contained a more definitive 435 nm shoulder corresponding to increased Chlorophyll content, and showed strong immuno-cross-reactivity with the CP47 antibody. The peak fractions off the column displayed a less prominent 435 nm shoulder, and did not cross-react with the antibody. Moreover, when a 6-Chlorophyll preparation was mixed with Sepharose beads coupled to CP47 antibody, the eluted material corresponded to a preparation of about 4 Chlorophylls per 2 pheophytins and did not show any cross- reaction with the antibody against CP47. The amount of CP47 protein in the 6-Chlorophyll preparation as quantitated using Coomassie Blue staining or from gel blots was sufficient to account for most of the extra 2 Chlorophylls. We conclude that D 1 -D2-cytochrome b559 preparations containing more than 4 Chlorophylls per 2 pheophytins can be contaminated with small amounts of CP47-D1 -D2-Cyt b559 complex and that native photosystem I1 reaction centers contain 4 core Chlorophylls per 2 pheophytins.
-
spectroscopic characterization of two forms of the d1 d2 cytochrome b559 complex from sugar beet
Photochemistry and Photobiology, 1993Co-Authors: Guillermo Montoya, Rafael Cases, Inmaculada Yruela, Rafael PicorelAbstract:Two D1-D2-cytochrome b559 complex forms, called RCIIa and RCIIb, with different pigment stoichi-ometry were characterized using absorption and surface-enhanced resonance Raman scattering spectroscopy and spectral gaussian deconvolution. Electronic absorption spectra of the RCIIb at 277 K showed significant differences compared to RCIIa, i.e. a strong decrease in the absorbance due to carotenoid and Chlorophyll for the same amount of pheophytin. A reduced carotenoid and Chlorophyll content in RCIIb was also observed in the surface-enhanced resonance Raman scattering spectra. Spectral deconvolution elicited three main absorption bands at 680, 672 and 669–670 nm, which were ascribed to P680, pheophytin and accessory Chlorophyll, respectively. In addition, a minor component around 667 nm was observed in the RCIIb, most probably due to some reaction center inactivation. Calculation of the relative area under the gaussians together with pigment stoichiometry data suggest that the 680, 672 and 669–670 nm components contain, respectively, two Chlorophylls, two pheophytins and four Chlorophylls for the RCIIa, and two Chlorophylls, two pheophytins and two Chlorophylls for the RCIIb.
Robert E. Blankenship - One of the best experts on this subject based on the ideXlab platform.
-
extinction coefficient for red shifted Chlorophylls Chlorophyll d and Chlorophyll f
Biochimica et Biophysica Acta, 2012Co-Authors: Nicholas Scales, Robert E. Blankenship, Robert D. Willows, Min ChenAbstract:Abstract Both Chlorophyll f and Chlorophyll d are red-shifted Chlorophylls in oxygenic photosynthetic organisms, which extend photon absorbance into the near infrared region. This expands the range of light that can be used to drive photosynthesis. Quantitative determination of Chlorophylls is a crucial step in the investigation of Chlorophyll-photosynthetic reactions in the field of photobiology and photochemistry. No methods have yet been worked out for the quantitative determination of Chlorophyll f . There is also no method available for the precise quantitative determination of Chlorophyll d although it was discovered in 1943. In order to obtain the extinction coefficients (e) of Chlorophyll f and Chlorophyll d , the concentrations of Chlorophylls were determined by Inductive Coupled Plasma Mass Spectrometry according to the fact that each Chlorophyll molecule contains one magnesium (Mg) atom. Molar extinction coefficient e chl f is 71.11 × 10 3 L mol − 1 A 707 nm cm − 1 and e chl d is 63.68 × 10 3 L mol − 1 A 697 nm cm − 1 in 100% methanol. This article is part of a Special Issue entitled: Photosynthesis Research for Sustainability: from Natural to Artificial.
-
expanding the solar spectrum used by photosynthesis
Trends in Plant Science, 2011Co-Authors: Min Chen, Robert E. BlankenshipAbstract:A limiting factor for photosynthetic organisms is their light-harvesting efficiency, that is the efficiency of their conversion of light energy to chemical energy. Small modifications or variations of Chlorophylls allow photosynthetic organisms to harvest sunlight at different wavelengths. Oxygenic photosynthetic organisms usually utilize only the visible portion of the solar spectrum. The cyanobacterium Acaryochloris marina carries out oxygenic photosynthesis but contains mostly Chlorophyll d and only traces of Chlorophyll a. Chlorophyll d provides a potential selective advantage because it enables Acaryochloris to use infrared light (700–750nm) that is not absorbed by Chlorophyll a. Recently, an even more red-shifted Chlorophyll termed Chlorophyll f has been reported. Here, we discuss using modified Chlorophylls to extend the spectral region of light that drives photosynthetic organisms.
-
Nomenclature for membrane-bound light-harvesting complexes of cyanobacteria
Photosynthesis Research, 2008Co-Authors: Min Chen, Yinan Zhang, Robert E. BlankenshipAbstract:Accessory Chlorophyll-binding proteins (CBP) in cyanobacteria have six transmembrane helices and about 11 conserved His residues that might participate in Chlorophyll binding. In various species of cyanobacteria, the CBP proteins bind different types of Chlorophylls, including Chlorophylls a, b, d and divinyl-Chlorophyll a, b . The CBP proteins do not belong to the light-harvesting complexes (LHC) superfamily of plant and algae. The proposed new name of CBP for this class of proteins, which is a unique accessory light-harvesting superfamily in cyanobacteria, clarifies the confusion of names of prochlorophytes Chlorophyll binding protein (Pcb), PSII-like light-harvesting proteins and iron-stress-induced protein A (IsiA). The CBP complexes are a member of a larger family that includes the Chlorophyll a -binding proteins CP43 and CP47 that function as core antennas of photosystem II.
Martin Grosjean - One of the best experts on this subject based on the ideXlab platform.
-
Quantification of Chlorophyll a, Chlorophyll b and pheopigments a in lake sediments through deconvolution of bulk UV–VIS absorption spectra
Journal of Paleolimnology, 2020Co-Authors: Andrea Sanchini, Martin GrosjeanAbstract:Assessments of aquatic paleoproduction and pigment preservation require accurate identification and quantification of sedimentary Chlorophylls. Using chromatographic techniques to analyze long records at high resolution is impractical because they are expensive and labor intensive. We have developed a new rapid and low-cost approach to infer the concentrations of Chlorophyll a , Chlorophyll b and related Chlorophyll derivatives (pheopigments a ) from the mathematical decomposition of UV–VIS measured bulk spectrophotometer absorption spectra of standard solutions and sediment extracts. We validated our method against high-performance liquid chromatography (HPLC) measurements on standard solutions and on varved, anoxic sediment from eutrophic Lake Lugano (Ponte Tresa sub-basin, southern Switzerland), where the history of productivity is relatively well known for the twentieth century. Our mathematical approach quantifies the concentration of Chlorophyll b ( $$ {\text{R}}_{{{\text{ad}}_{\text{J}}}}^{2} $$ R ad J 2 = 0.99, RMSEP ~ 5.9%), Chlorophyll a ( $$ {\text{R}}_{{{\text{ad}}_{\text{J}}}}^{2} $$ R ad J 2 = 0.98, RMSEP ~ 5.0%), and pyropheophorbide a ( $$ {\text{R}}_{{{\text{ad}}_{\text{J}}}}^{2} $$ R ad J 2 = 0.99, RMSEP ~ 7.8%) in standard solutions. We obtain comparable results for total chloropigment a (Chlorophyll a + pheopigments a ), Chlorophyll a and diagenetic products (pheopigments a ) in the sediment samples of our case study (Ponte Tresa). Here, HPLC concentrations of Chlorophyll b are very low. The method has, however, the potential to achieve values for Chlorophyll b concentrations in sediments with Chlorophylls a /Chlorophylls b ratios lower than 3.4. The pigment stratigraphy of the Ponte Tresa sediments correspond very well with the paleoproduction and eutrophication history of the twentieth century. The ratio between Chlorophyll a and pheopigments a used as a qualitative indicator of sedimentary Chlorophyll preservation (Chlorophyll a /{Chlorophyll a + pheopigments a }) is only weakly correlated with aquatic paleoproduction (r_adj = 0.35, p -value = 0.045) and remained remarkably constant in the recent century despite strong anthropogenic eutrophication. The new method is useful for obtaining, in a cost- and time-efficient way, information about major sedimentary pigment groups that are relevant to inferring paleoproduction, potentially green algae biomass, pigment preservation and early diagenetic effects.
Robert J. Porra - One of the best experts on this subject based on the ideXlab platform.
-
The derivation of the formyl‐group oxygen of Chlorophyll b in higher plants from molecular oxygen
FEBS Journal, 2005Co-Authors: Robert J. Porra, Wolfram Schäfer, Edmund Cmiel, Ingrid Katheder, Hugo ScheerAbstract:The mechanism of formation of the formyl group of Chlorophyll b has long been obscure but, in this paper, the origin of the 7-formyl-group oxygen of Chlorophyll b in higher plants was determined by greening etiolated maize leaves, excised from dark-grown plants, by illumination under white light in the presence of either H218O or 18O2 and examining the newly synthesized Chlorophylls by mass spectroscopy. To minimize the possible loss of 18O label from the 7-formyl substituent by reversible formation of Chlorophyll b-71-gem-diol (hydrate) with unlabelled water in the cell, the formyl group was reduced to a hydroxymethyl group during extraction with methanol containing NaBH4: Chlorophyll a remained unchanged during this rapid reductive extraction process. Mass spectra of Chlorophyll a and [7-hydroxymethyl]-Chlorophyll b extracted from leaves greened in the presence of either H218O or 18O2 revealed that 18O was incorporated only from molecular oxygen but into both Chlorophylls: the mass spectra were consistent with molecular oxygen providing an oxygen atom not only for incorporation into the 7-formyl group of Chlorophyll b but also for the well-documented incorporation into the 131-oxo group of both Chlorophylls a and b [see Walker, C. J., Mansfield, K. E., Smith, K. M. & Castelfranco, P. A. (1989) Biochem. J. 257, 599–602]. The incorporation of isotope led to as much as 77% enrichment of the 131-oxo group of Chlorophyll a: assuming identical incorporation into the 131 oxygen of Chlorophyll b, then enrichment of the 7-formyl oxygen was as much as 93%. Isotope dilution by re-incorporation of photosynthetically produced oxygen from unlabelled water was negligible as shown by a greening experiment in the presence of 3-(3,4-dichlorophenyl)-1,1-dimethylurea. The high enrichment using 18O2, and the absence of labelling by H218O, unequivocally demonstrates that molecular oxygen is the sole precursor of the 7-formyl oxygen of Chlorophyll b in higher plants and strongly suggests a single pathway for the formation of the Chlorophyll b formyl group involving the participation of an oxygenase-type enzyme.
-
the chequered history of the development and use of simultaneous equations for the accurate determination of Chlorophylls a and b
Photosynthesis Research, 2002Co-Authors: Robert J. PorraAbstract:Over the last half century, the most frequently used assay for Chlorophylls in higher plants and green algae, the Arnon assay [Arnon DI (1949) Plant Physiol 24: 1–15], employed simultaneous equations for determining the concentrations of Chlorophylls a and b in aqueous 80% acetone extracts of Chlorophyllous plant and algal materials. These equations, however, were developed using extinction coefficients for Chlorophylls a and b derived from early inaccurate spectrophotometric data. Thus, Arnon’s equations give inaccurate Chlorophyll a and b determinations and, therefore, inaccurate Chlorophyll a/b ratios, which are always low. This paper describes how the ratios are increasingly and alarmingly low as the proportion of Chlorophyll a increases. Accurate extinction coefficients for Chlorophylls a and b, and the more reliable simultaneous equations derived from them, have been published subsequently by many research groups; these new post-Arnon equations, however, have been ignored by many researchers. This Minireview records the history of the development of accurate simultaneous equations and some difficulties and anomalies arising from the retention of Arnon’s seriously flawed equations.
-
the derivation of the formyl group oxygen of Chlorophyll b in higher plants from molecular oxygen
FEBS Journal, 1994Co-Authors: Robert J. Porra, Wolfram Schäfer, Edmund Cmiel, Ingrid Katheder, Hugo ScheerAbstract:The mechanism of formation of the formyl group of Chlorophyll b has long been obscure but, in this paper, the origin of the 7-formyl-group oxygen of Chlorophyll b in higher plants was determined by greening etiolated maize leaves, excised from dark-grown plants, by illumination under white light in the presence of either H218O or 18O2 and examining the newly synthesized Chlorophylls by mass spectroscopy. To minimize the possible loss of 18O label from the 7-formyl substituent by reversible formation of Chlorophyll b-71-gem-diol (hydrate) with unlabelled water in the cell, the formyl group was reduced to a hydroxymethyl group during extraction with methanol containing NaBH4: Chlorophyll a remained unchanged during this rapid reductive extraction process. Mass spectra of Chlorophyll a and [7-hydroxymethyl]-Chlorophyll b extracted from leaves greened in the presence of either H218O or 18O2 revealed that 18O was incorporated only from molecular oxygen but into both Chlorophylls: the mass spectra were consistent with molecular oxygen providing an oxygen atom not only for incorporation into the 7-formyl group of Chlorophyll b but also for the well-documented incorporation into the 131-oxo group of both Chlorophylls a and b [see Walker, C. J., Mansfield, K. E., Smith, K. M. & Castelfranco, P. A. (1989) Biochem. J. 257, 599–602]. The incorporation of isotope led to as much as 77% enrichment of the 131-oxo group of Chlorophyll a: assuming identical incorporation into the 131 oxygen of Chlorophyll b, then enrichment of the 7-formyl oxygen was as much as 93%. Isotope dilution by re-incorporation of photosynthetically produced oxygen from unlabelled water was negligible as shown by a greening experiment in the presence of 3-(3,4-dichlorophenyl)-1,1-dimethylurea. The high enrichment using 18O2, and the absence of labelling by H218O, unequivocally demonstrates that molecular oxygen is the sole precursor of the 7-formyl oxygen of Chlorophyll b in higher plants and strongly suggests a single pathway for the formation of the Chlorophyll b formyl group involving the participation of an oxygenase-type enzyme.
-
The Unexpected Reduction of the Vinyl Group of Chlorophyll b by Sodium Borohydride in Methanolic Extracts of Maize Leaves and Its Inhibition by 8-Hydroxyquinoline
Zeitschrift für Naturforschung C, 1993Co-Authors: Robert J. Porra, Wolfram Schäfer, Edmund Cmiel, Ingrid Katheder, Hugo ScheerAbstract:During rapid extraction of Chlorophylls from maize leaves under reducing conditions with methanol containing NaBH₄, Chlorophyll a remained unchanged but Chlorophyll b yielded [7-hydroxymethyl]-Chlorophyll b. The 3-vinyl group of Chlorophyll b was also reduced forming significant am ounts, up to 60%, of [3-ethyl]-[7-hydroxymethyl]-Chlorophyll b. This was unexpected since this reduction of the 3-vinyl group does not occur when isolated Chlorophyll b is treated in an identical manner with methanolic borohydride. The vinyl-group of Chlorophyll a is not reduced during the same extraction conditions suggesting that the presence of a formyl or hydroxyethyl group at C-7 is necessary. The presence of 8-hydroxyquinoline and NaBH₄ in equimolar (16.5 m M) concentrations strongly inhibits the reduction of the 3-vinyl group of Chlorophyll b in leaf extracts