Determination of the primary charge separation rate in Photosystem II reaction centers at 15 K

Michael R Wasielewski, Douglas G. Johnson, Govindjee, Christopher Preston, Michael Seibert

Research output: Contribution to journalArticle

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Abstract

We have measured the rate constant for the formation of the oxidized chlorophyll a electron donor (P680+) and the reduced electron acceptor pheophytin a- (Pheo a-) following excitation of isolated Photosystem II reaction centers (PS II RC) at 15 K. This PS II RC complex consists of D1, D2, and cytochrome b-559 proteins and was prepared by a procedure which stabilizes the protein complex. Transient absorption difference spectra were measured from 450-840 nm as a function of time with 500fs resolution following 610 nm laser excitation. The formation of P680+-Pheo a- is indicated by the appearance of a band due to P680+ at 820 nm and corresponding absorbance changes at 490, 515 and 546 nm due to the formation of Pheo a-. The appearance of the 490 nm and 820 nm bands is monoexponenital with τ=1.4±0.2 ps. Treatment of the PS II RC with sodium dithionite and methyl viologen followed by exposure to laser excitation results in accumulation of Pheo a-. Laser excitation of these prereduced RCs at 15 K results in formation of a transient absorption spectrum assigned to 1*P680. We observe wavelength-dependent kinetics for the recovery of the transient bleach of the Qy absorption bands of the pigments in both untreated and pre-reduced PS II RCs at 15K. This result is attributed to an energy transfer process within the PS II RC at low temperature that is not connected with charge separation.

Original languageEnglish
Pages (from-to)89-99
Number of pages11
JournalPhotosynthesis Research
Volume22
Issue number1
DOIs
Publication statusPublished - Jan 1989

Fingerprint

Photosystem II Protein Complex
photosystem II
Laser excitation
Lasers
lasers
Absorption spectra
electrons
Electrons
Dithionite
Paraquat
paraquat
Energy Transfer
energy transfer
cytochrome b
Pigments
Energy transfer
absorbance
wavelengths
Rate constants
Proteins

Keywords

  • electron transfer
  • picosecond spectroscopy
  • PS II reaction centers

ASJC Scopus subject areas

  • Plant Science

Cite this

Determination of the primary charge separation rate in Photosystem II reaction centers at 15 K. / Wasielewski, Michael R; Johnson, Douglas G.; Govindjee; Preston, Christopher; Seibert, Michael.

In: Photosynthesis Research, Vol. 22, No. 1, 01.1989, p. 89-99.

Research output: Contribution to journalArticle

Wasielewski, Michael R ; Johnson, Douglas G. ; Govindjee ; Preston, Christopher ; Seibert, Michael. / Determination of the primary charge separation rate in Photosystem II reaction centers at 15 K. In: Photosynthesis Research. 1989 ; Vol. 22, No. 1. pp. 89-99.
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AB - We have measured the rate constant for the formation of the oxidized chlorophyll a electron donor (P680+) and the reduced electron acceptor pheophytin a- (Pheo a-) following excitation of isolated Photosystem II reaction centers (PS II RC) at 15 K. This PS II RC complex consists of D1, D2, and cytochrome b-559 proteins and was prepared by a procedure which stabilizes the protein complex. Transient absorption difference spectra were measured from 450-840 nm as a function of time with 500fs resolution following 610 nm laser excitation. The formation of P680+-Pheo a- is indicated by the appearance of a band due to P680+ at 820 nm and corresponding absorbance changes at 490, 515 and 546 nm due to the formation of Pheo a-. The appearance of the 490 nm and 820 nm bands is monoexponenital with τ=1.4±0.2 ps. Treatment of the PS II RC with sodium dithionite and methyl viologen followed by exposure to laser excitation results in accumulation of Pheo a-. Laser excitation of these prereduced RCs at 15 K results in formation of a transient absorption spectrum assigned to 1*P680. We observe wavelength-dependent kinetics for the recovery of the transient bleach of the Qy absorption bands of the pigments in both untreated and pre-reduced PS II RCs at 15K. This result is attributed to an energy transfer process within the PS II RC at low temperature that is not connected with charge separation.

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