PARENT SESSION

Symposium S2A Type I reaction centres
Monday August 30th, 2004 2:40 PM-4:40 PM Room 511D
Chair: John Golbeck
Co-Chair: Kevin Redding

A₁ reduction in intact cyanobacterial Photosystem I studied using time-resolved step-scan fourier transform infra-red difference spectroscopy in combination with isotope labeling and quinone exchange experiments. Gary Hastings^*,1, Velautham Sivakumar¹, ¹ Department of Physics and Astronomy, Atlanta, GA, USA

ABSTRACT- Time-resolved step-scan Fourier transform infrared difference spectroscopy (TRSS FTIR DS) has been used to produce (A₁ ^- -A₁) FTIR difference spectra in intact PS I particles from S. 7002 and S. 6803 at 77 K. (A₁^--A₁) FTIR difference spectra were also obtained using fully deuterated PS I particles from S. 7002, and uniformly ¹⁵N and ¹³C labeled PS I particles from S. 6803. Comparison of (A₁^--A₁) FTIR difference spectra obtained using the non-labeled and variously labeled PS I particles allowed clear assignments of many of the bands in the difference spectra. Amide I and II protein vibrations are identified, as are quinone and semiquinone C=O and C=C modes. Bands in the (A₁^--A₁) FTIR difference spectra are also found to be associated with the 13³ ester and 13¹ keto C=O groups of A₀. Thus A₁ reduction perturbs A₀, probably via a long range electrostatic interaction. Finally, spectra are also presented for PS I particles from S. 6803 in which plastoquinone-9 (as opposed to phylloquinone) occupies the A₁ binding site.

KEY WORDS: Time resolved Step scan FTIR, A1, FTIR, Photosystem I