A Difference Fourier transform infrared study of tyrosyl radical Z* decay in photosystem II.
Photosystem II (PSII) contains a redox-active tyrosine, Z* Difference Fourier transform infrared (FTIR) spectroscopy can be used to obtain structural information about this species, which is a neutral radical, Z*, in the photooxidized form. Previously, we have used isotopic labeling, inhibitors, and site-directed mutagenesis to assign a vibrational line at 1478 cm(-1) to Z*; these studies were performed on highly resolved PSII preparations at pH 7.5, under conditions where Q(A)(-) and Q(B)(-) make no detectable contribution to the vibrational spectrum (Kim, Ayala, Steenhuis, Gonzalez, Razeghifard, and Barry. 1998. Biochim. Biophys. Acta. 1366:330-354). Here, time-resolved infrared data associated with the reduction of tyrosyl radical Z* were acquired from spinach core PSII preparations at pH 6.0. Electron paramagnetic resonance spectroscopy and fluorescence control experiments were employed to measure the rate of Q(A)(-) and Z* decay. Q(B)(-) did not recombine with Z* under these conditions. Difference FTIR spectra, acquired over this time regime, exhibited time-dependent decreases in the amplitude of a 1478 cm(-1) line. Quantitative comparison of the rates of Q(A)(-) and Z* decay with the decay of the 1478 cm(-1) line supported the assignment of a 1478 cm(-1) component to Z*. Comparison with difference FTIR spectra obtained from PSII samples, in which tyrosine is labeled, supported this conclusion and identified other spectral components assignable to Z* and Z. To our knowledge, this is the first kinetic study to use quantitative comparison of kinetic constants in order to assign spectral features to Z*.
Ayala
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Department of Biochemistry, Molecular Biology, and Biophysics, University of Minnesota, St. Paul, Minnesota 55108-1022, USA.
Kim
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S
Barry
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BA
D000458:Cyanobacteria / Q000737:chemistry; D004578:Electron Spin Resonance Spectroscopy; D005609:Free Radicals / Q000737:chemistry / Q000378:metabolism; D006207:Half-Life; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008027:Light; D008345:Manganese / Q000378:metabolism; D010084:Oxidation-Reduction; D045322:Photosynthetic Reaction Center Complex Proteins / Q000737:chemistry / Q000378:metabolism*; D045332:Photosystem II Protein Complex; D013050:Spectrometry, Fluorescence; D017550:Spectroscopy, Fourier Transform Infrared; D018724:Spinacia oleracea / Q000737:chemistry / Q000166:cytology; D013696:Temperature; D014443:Tyrosine / Q000031:analogs & derivatives* / Q000737:chemistry / Q000378:metabolism; D014732:Vibration
D005609:Free Radicals; D045322:Photosynthetic Reaction Center Complex Proteins; D045332:Photosystem II Protein Complex; C114979:tyrosyl radical YZ; D014443:Tyrosine; D008345:Manganese