Chlorophyll Function in the Photosynthetic Reaction Center

Katz, Joseph; Norris, James R.; Shipman, Lester L.; Thurnauer, Marion C.; Wasielewski, Michael R.

doi:10.1146/annurev.bb.07.060178.002141

Cited by 156 publications

(88 citation statements)

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“…A mechanism currently assumed in bacterial photosynthesis (1)(2)(3)(4)(5)(6) involves electron transfer between an electronically excited bacteriochlorophyll special pair (Bchl)2* and a bacteriopheophytin (Bph), followed by electron transfer to an ironubiquinone complex FeQ, [1.4] in which T denotes a triplet state and (Bchl)2 is the ground state singlet, have led to an estimate of the spin exchange integral for the radical pair in [1.1] and, in turn, to the electron transfer integral for [1.1]. A discrepancy then arises in the calculated compared to the experimental electron transfer rate.…”

Section: Introductionmentioning

confidence: 99%

“…A discrepancy then arises in the calculated compared to the experimental electron transfer rate. There are several possible explanations, one of which is explored in the present paper: There are one (Bchl)2, two Bchls, and two Bphs in the reaction center (1)(2)(3)(4)(5)(6). We consider a possible hopping of the electron (or hole) in the (Bchl)2+Bph-pair between two sites.…”

Section: Introductionmentioning

confidence: 99%

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On spin-exchange and electron-transfer rates in bacterial photosynthesis

Haberkorn

Michel‐Beyerle

Marcus

1979

Proc. Natl. Acad. Sci. U.S.A.

118

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A discrepancy is explored regarding the spin exchange integral estimated from magnetic field effects on recombination of the bacteriochlorophyll dimer cation (Bchl)2+ and the bacteriopheophytin anion Bph-and the measured electron transfer rate between Bph and electronically excited (Bchl)2. In one explanation considered here there are two sites for the electron or for the hole, with a hopping between sites.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

On spin-exchange and electron-transfer rates in bacterial photosynthesis

Haberkorn

Michel‐Beyerle

Marcus

1979

Proc. Natl. Acad. Sci. U.S.A.

118

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“…The optical changes associated with the oxidations of P-700 and P-680 (18-24), particularly an enhanced absorption at -820 nm, and the electron spin resonance (ESR) linewidths and g-values (10, [24][25][26][27][28][29][30][31][32] are characteristic of Chl ir cation radicals (33). ESR (10,(25)(26), ENDOR (electron-nuclear double resonance) (34-35), optical, and circular dichroism (36) results have further established the dimeric or "special pair" nature of P-700+ . ESR data show (25) that the 7 G (1 G = 1o-4 tesla) peak-to-peak linewidth (AH) of P-700+ is narrower by V-than that of Chl+-(AH = 9 G) in dichloromethane and dichloromethane/methanol solutions, as expected if the unpaired electron of the radical is equally shared between two Chl molecules.…”

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confidence: 98%

Ligated chlorophyll cation radicals: Their function in photosystem II of plant photosynthesis

Davis

Forman

Fajer

1979

Proc. Natl. Acad. Sci. U.S.A.

166

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Magnesium tetraphenylchlorin, a synthetic model for chlorophyll, exhibits significant variations in the unpaired spin densities of its cation radicals with concomitant changes in oxidation potentials as a function of solvent and axial ligand. Similar effects are observed for chlorophyll (Chl) a and its cation radicals. Oxidation potentials for Chl -Chl+' as high as +0.9 V (against a normal hydrogen electrode) are observed in nonaqueous solvents, with linewidths of the electron spin resonance signals of monomeric Chl+' ranging between 9.2 and 7.8 G in solution. These changes in electronic configuration and ease of oxidation are attributed to mixing of two nearly degenerate ground states of the radicals theoretically predicted by molecular orbital calculations. Comparison of the properties of chlorophyll in vitro with the optical, redox, and magnetic characteristics attributed to P680, the primary donor of photosystem II which mediates oxygen evolution in plant photosynthesis, leads us to suggest that P480 may be a ligated chlorophyll monomer whose function as a phototrap is determined by interactions with its (protein?) environment. Photosynthesis in algae and green plants functions via two chlorophyll (Chl)-mediated systems that cooperatively oxidize water (photosystem II, PS II) and reduce carbon dioxide (PS I) (1-14). The primary chemical products generated by the light harvested by the antenna network and funnelled to the reaction centers are believed to be oxidized Chls, P-700+ in PS I and P-680+-in PS II1(1-14), and reduced Chl or pheophytin (11,(15)(16)(17). The optical changes associated with the oxidations of P-700 and P-680 (18-24), particularly an enhanced absorption at -820 nm, and the electron spin resonance (ESR) linewidths and g-values (10, [24][25][26][27][28][29][30][31][32] are characteristic of Chl ir cation radicals (33). ESR (10,(25)(26), ENDOR (electron-nuclear double resonance) (34-35), optical, and circular dichroism (36) results have further established the dimeric or "special pair" nature of P-700+ . ESR data show (25) that the 7 G (1 G = 1o-4 tesla) peak-to-peak linewidth (AH) of P-700+ is narrower by V-than that of Chl+-(AH = 9 G) in dichloromethane and dichloromethane/methanol solutions, as expected if the unpaired electron of the radical is equally shared between two Chl molecules. Additional support for delocalization of spin over two Chls in P-700+-derives from ENDOR spectra of oxidized chloroplasts (34,35) in which several proton hyperfine splittings are found to be approximately half those of Chl+-in vitro (37,38). The nature of P-680+' in PS II is considerably more ambiguous: linewidths of ESR signals attributed to P-680+-range from 7 to 9 G (27-32), resulting in proposals of monomer (28), dimer (29-31), and even trimer (32) configurations. Even more puzzling are the large differences in oxidation potentials of P-700 and P-680. Titrations of P-700 yield a midpoint potential (39-41) ranging between +0.4 and +0.5 V against the normal hydrogen electrode, whereas the minimu...

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“…Klorofil-a berfungsi mengubah cahaya matahari menjadi energi kimia (Hunt, 2000) di mana semakin tinggi klorofil-a maka produktivitas primernya akan semakin tinggi (Mantyla et al, 1995). Klorofil-a berperan dalam penyerapan cahaya matahari, transfer, dan perubahan energi menjadi bentuk yang dapat digunakan oleh organisme (Katz et al, 1978). Efisiensi penggunaan cahaya matahari oleh fitoplankton dalam proses fotosintesis juga didukung oleh konsentrasi klorofil-a (Furuya et al, 1998 Fluktuasi efisiensi fotosintesis pada suatu badan air sangat besar, baik secara musiman maupun secara vertikal pada zona eufotik (Vait, 1972).…”

Section: Hasil Dan Bahasanunclassified

Efisiensi Pemanfaatanenergicahayamatahariolehfitoplankton Dalamproses Fotosintesisdiwadukmalahayu

Warsa¹,

Purnomo²

2017

BAWAL Widya Riset Perikanan Tangkap

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ABSTRAKCahaya matahari merupakan sumber energi utama yang menentukan produktivitas suatu ekosistem akuatik. Ketersediaan cahaya akan menentukan kecepatan fotosintesis yang akan menentukan kecepatan pertumbuhan produsen primer. Tujuan penelitian ini adalah untuk mengetahui efisiensi pemanfaatan cahaya matahari oleh fitoplankton di Waduk Malahayu. Penelitian ini dilakukan di Waduk Malahayu, Kabupaten Brebes, Jawa Barat, pada bulan Oktober 2010. Pengamatan produktivitas primer kotor, kelimpahan fitoplankton, intensitas cahaya, dan klorofil-a dilakukan pada dua stasiun yaitu stasiun keramba jaring apung dan dam pada kedalaman 0,5; 2; dan 4 m dengan metode survei berstrata. Pengukuran produktivitas primer kotor dilakukan dengan metode botol gelap dan terang. Hasil penelitian menunjukkan nilai produktivitas primer kotor di Waduk Malahayu berkisar 45,6-121,9 mgC/jam dan konsentrasi klorofil-a berkisar 3,7-11,8 mg/m 3 . Kelimpahan individu fitoplankton di Waduk Malahayu berkisar 100,6-112,67 ind./l dengan genera yang dominan adalah Oscillatoria (Cyanophyceae) dan Peridinium (Dinophyceae). Efisiensi penggunaan cahaya matahari oleh fitoplankton di Waduk Malahayu berkisar 0,5-2,7%. Efisiensi cahaya matahari menurun dengan bertambahnya kedalaman air.

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Chlorophyll Function in the Photosynthetic Reaction Center

Cited by 156 publications

References 0 publications

On spin-exchange and electron-transfer rates in bacterial photosynthesis

On spin-exchange and electron-transfer rates in bacterial photosynthesis

Ligated chlorophyll cation radicals: Their function in photosystem II of plant photosynthesis

Efisiensi Pemanfaatanenergicahayamatahariolehfitoplankton Dalamproses Fotosintesisdiwadukmalahayu

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