Abstract
Photosystem II (PSII) contains two accessory chlorophylls (ChlZ, ligated to D1-His118, and ChlD, ligated to D2-His117), carotenoid (Car), and heme (cytochrome b559) cofactors that function as alternate electron donors under conditions in which the primary electron-donation pathway from the O2-evolving complex to P680+ is inhibited. The photooxidation of the redox-active accessory chlorophylls and Car has been characterized by near-infrared (near-IR) absorbance, shifted-excitation Raman difference spectroscopy (SERDS), and electron paramagnetic resonance (EPR) spectroscopy over a range of cryogenic temperatures from 6 to 120 K in both Synechocystis PSII core complexes and spinach PSII membranes. The following key observations were made: (1) only one Chl+ near-IR band is observed at 814 nm in Synechocystis PSII core complexes, which is assigned to ChlZ + based on previous spectroscopic studies of the D1-H118Q and D2-H117Q mutants [Stewart, D. H., Cua, A., Chisholm, D. A., Diner, B. A., Bocian, D. F., and Brudvig, G. W. (1998) Biochemistry 37, 10040-10046]; (2) two Chl+ near-IR bands are observed at 817 and 850 nm in spinach PSII membranes which are formed with variable relative yields depending on the illumination temperature and are assigned to ChlZ +, and ChlD +, respectively; (3) the Chl and Car cation radicals have significantly different stabilities at reduced temperatures with Car+ decaying much faster; (4) in Synechocystis PSII core complexes, Car+ decays by recombination with QA - and not by ChlZ/ChlD oxidation, with multiphasic kinetics that are attributed to an ensemble of protein conformers that are trapped as the protein is frozen; and (5) in spinach PSII membranes, Car+ decays mainly by recombination with QA -, but also partly by formation of the 850 nm Chl cation radical. The greater stability of ChlZ + at low temperatures enabled us to confirm that resonance Raman bands previously assigned to ChlZ + are correctly assigned. In addition, the formation and decay of these cations provide insight into the alternate electron-donation pathways to P680+.
| Original language | English |
|---|---|
| Pages (from-to) | 193-203 |
| Number of pages | 11 |
| Journal | Biochemistry |
| Volume | 40 |
| Issue number | 1 |
| DOIs | |
| Publication status | Published - Jan 9 2001 |
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Characterization of carotenoid and chlorophyll photooxidation in photosystem II. / Tracewell, C. A.; Cua, A.; Stewart, D. H.; Bocian, D. F.; Brudvig, Gary W.
In: Biochemistry, Vol. 40, No. 1, 09.01.2001, p. 193-203.Research output: Contribution to journal › Article
}
TY - JOUR
T1 - Characterization of carotenoid and chlorophyll photooxidation in photosystem II
AU - Tracewell, C. A.
AU - Cua, A.
AU - Stewart, D. H.
AU - Bocian, D. F.
AU - Brudvig, Gary W
PY - 2001/1/9
Y1 - 2001/1/9
N2 - Photosystem II (PSII) contains two accessory chlorophylls (ChlZ, ligated to D1-His118, and ChlD, ligated to D2-His117), carotenoid (Car), and heme (cytochrome b559) cofactors that function as alternate electron donors under conditions in which the primary electron-donation pathway from the O2-evolving complex to P680+ is inhibited. The photooxidation of the redox-active accessory chlorophylls and Car has been characterized by near-infrared (near-IR) absorbance, shifted-excitation Raman difference spectroscopy (SERDS), and electron paramagnetic resonance (EPR) spectroscopy over a range of cryogenic temperatures from 6 to 120 K in both Synechocystis PSII core complexes and spinach PSII membranes. The following key observations were made: (1) only one Chl+ near-IR band is observed at 814 nm in Synechocystis PSII core complexes, which is assigned to ChlZ + based on previous spectroscopic studies of the D1-H118Q and D2-H117Q mutants [Stewart, D. H., Cua, A., Chisholm, D. A., Diner, B. A., Bocian, D. F., and Brudvig, G. W. (1998) Biochemistry 37, 10040-10046]; (2) two Chl+ near-IR bands are observed at 817 and 850 nm in spinach PSII membranes which are formed with variable relative yields depending on the illumination temperature and are assigned to ChlZ +, and ChlD +, respectively; (3) the Chl and Car cation radicals have significantly different stabilities at reduced temperatures with Car+ decaying much faster; (4) in Synechocystis PSII core complexes, Car+ decays by recombination with QA - and not by ChlZ/ChlD oxidation, with multiphasic kinetics that are attributed to an ensemble of protein conformers that are trapped as the protein is frozen; and (5) in spinach PSII membranes, Car+ decays mainly by recombination with QA -, but also partly by formation of the 850 nm Chl cation radical. The greater stability of ChlZ + at low temperatures enabled us to confirm that resonance Raman bands previously assigned to ChlZ + are correctly assigned. In addition, the formation and decay of these cations provide insight into the alternate electron-donation pathways to P680+.
AB - Photosystem II (PSII) contains two accessory chlorophylls (ChlZ, ligated to D1-His118, and ChlD, ligated to D2-His117), carotenoid (Car), and heme (cytochrome b559) cofactors that function as alternate electron donors under conditions in which the primary electron-donation pathway from the O2-evolving complex to P680+ is inhibited. The photooxidation of the redox-active accessory chlorophylls and Car has been characterized by near-infrared (near-IR) absorbance, shifted-excitation Raman difference spectroscopy (SERDS), and electron paramagnetic resonance (EPR) spectroscopy over a range of cryogenic temperatures from 6 to 120 K in both Synechocystis PSII core complexes and spinach PSII membranes. The following key observations were made: (1) only one Chl+ near-IR band is observed at 814 nm in Synechocystis PSII core complexes, which is assigned to ChlZ + based on previous spectroscopic studies of the D1-H118Q and D2-H117Q mutants [Stewart, D. H., Cua, A., Chisholm, D. A., Diner, B. A., Bocian, D. F., and Brudvig, G. W. (1998) Biochemistry 37, 10040-10046]; (2) two Chl+ near-IR bands are observed at 817 and 850 nm in spinach PSII membranes which are formed with variable relative yields depending on the illumination temperature and are assigned to ChlZ +, and ChlD +, respectively; (3) the Chl and Car cation radicals have significantly different stabilities at reduced temperatures with Car+ decaying much faster; (4) in Synechocystis PSII core complexes, Car+ decays by recombination with QA - and not by ChlZ/ChlD oxidation, with multiphasic kinetics that are attributed to an ensemble of protein conformers that are trapped as the protein is frozen; and (5) in spinach PSII membranes, Car+ decays mainly by recombination with QA -, but also partly by formation of the 850 nm Chl cation radical. The greater stability of ChlZ + at low temperatures enabled us to confirm that resonance Raman bands previously assigned to ChlZ + are correctly assigned. In addition, the formation and decay of these cations provide insight into the alternate electron-donation pathways to P680+.
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U2 - 10.1021/bi001992o
DO - 10.1021/bi001992o
M3 - Article
VL - 40
SP - 193
EP - 203
JO - Biochemistry
JF - Biochemistry
SN - 0006-2960
IS - 1
ER -