Abstract
We report the continuous power saturation and temperature dependence of three EPR signals which are generated by low-temperature illumination of dark-adapted Photosystem II (PSII) membranes and are associated with the S2 state of the O2-evolving complex of photosynthesis. PSII membranes which are dark-adapted for 4 h at 0°C and illuminated at 200 K for 2 min exhibit a S2 state EPR signal which saturates easily (P1/2 = 3.7 mW at 6.0 K) and has an intensity maximum at 6.9 K under nonsaturating conditions. The S2 state EPR signal obtained from 6-min dark-incubated samples illuminated at 160 K exhibits no intensity maximum in the 4.0-16.0 K range under nonsaturating conditions and saturates at higher microwave powers (P1/2 = 37.1 mW at 6.0 K). Finally, a third signal produced by 170 K illumination of 6-min dark-adapted membranes shows an intensity maximum at 5.9 K under nonsaturating conditions and is not saturated with our current experimental setup (P1/2 > 156 mW at 6.0 K). We conclude that each EPR spectrum originates from a thermally excited state of one of three distinct configurations of the manganese complex which is believed to make up the active site. The temperature dependence data are fitted to a model in which two paramagnetic sites are ferromagnetically exchange coupled. All three sets of data can be accounted for by varying the magnitude of the superexchange coupling constant.
| Original language | English |
|---|---|
| Pages (from-to) | 2643-2648 |
| Number of pages | 6 |
| Journal | Journal of the American Chemical Society |
| Volume | 107 |
| Issue number | 9 |
| Publication status | Published - 1985 |
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Magnetic properties of manganese in the photosynthetic O2- evolving complex. / De Paula, Julio C.; Brudvig, Gary W.
In: Journal of the American Chemical Society, Vol. 107, No. 9, 1985, p. 2643-2648.Research output: Contribution to journal › Article
}
TY - JOUR
T1 - Magnetic properties of manganese in the photosynthetic O2- evolving complex
AU - De Paula, Julio C.
AU - Brudvig, Gary W
PY - 1985
Y1 - 1985
N2 - We report the continuous power saturation and temperature dependence of three EPR signals which are generated by low-temperature illumination of dark-adapted Photosystem II (PSII) membranes and are associated with the S2 state of the O2-evolving complex of photosynthesis. PSII membranes which are dark-adapted for 4 h at 0°C and illuminated at 200 K for 2 min exhibit a S2 state EPR signal which saturates easily (P1/2 = 3.7 mW at 6.0 K) and has an intensity maximum at 6.9 K under nonsaturating conditions. The S2 state EPR signal obtained from 6-min dark-incubated samples illuminated at 160 K exhibits no intensity maximum in the 4.0-16.0 K range under nonsaturating conditions and saturates at higher microwave powers (P1/2 = 37.1 mW at 6.0 K). Finally, a third signal produced by 170 K illumination of 6-min dark-adapted membranes shows an intensity maximum at 5.9 K under nonsaturating conditions and is not saturated with our current experimental setup (P1/2 > 156 mW at 6.0 K). We conclude that each EPR spectrum originates from a thermally excited state of one of three distinct configurations of the manganese complex which is believed to make up the active site. The temperature dependence data are fitted to a model in which two paramagnetic sites are ferromagnetically exchange coupled. All three sets of data can be accounted for by varying the magnitude of the superexchange coupling constant.
AB - We report the continuous power saturation and temperature dependence of three EPR signals which are generated by low-temperature illumination of dark-adapted Photosystem II (PSII) membranes and are associated with the S2 state of the O2-evolving complex of photosynthesis. PSII membranes which are dark-adapted for 4 h at 0°C and illuminated at 200 K for 2 min exhibit a S2 state EPR signal which saturates easily (P1/2 = 3.7 mW at 6.0 K) and has an intensity maximum at 6.9 K under nonsaturating conditions. The S2 state EPR signal obtained from 6-min dark-incubated samples illuminated at 160 K exhibits no intensity maximum in the 4.0-16.0 K range under nonsaturating conditions and saturates at higher microwave powers (P1/2 = 37.1 mW at 6.0 K). Finally, a third signal produced by 170 K illumination of 6-min dark-adapted membranes shows an intensity maximum at 5.9 K under nonsaturating conditions and is not saturated with our current experimental setup (P1/2 > 156 mW at 6.0 K). We conclude that each EPR spectrum originates from a thermally excited state of one of three distinct configurations of the manganese complex which is believed to make up the active site. The temperature dependence data are fitted to a model in which two paramagnetic sites are ferromagnetically exchange coupled. All three sets of data can be accounted for by varying the magnitude of the superexchange coupling constant.
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M3 - Article
VL - 107
SP - 2643
EP - 2648
JO - Journal of the American Chemical Society
JF - Journal of the American Chemical Society
SN - 0002-7863
IS - 9
ER -