Time-resolved Fourier transform infrared difference spectroscopy for the study of A1 reduction in intact photosystem I.

Abstract

Time-resolved-step-scan Fourier transform infrared and visible absorption difference spectroscopy, with nanosecond to millisecond time-resolution has been applied to the study of photosystem I particles from Synechocystis sp. 6803. From these studies a time-resolved FTIR difference spectrum associated with reduction of A1 in photosystem I [(A1--A1)] has been obtained using PS I particles under physiological conditions. Previously we have reported a static (A1--A1) FTIR difference spectrum obtained using PS I particles that have been stripped of all the iron sulfur clusters, and we were unable to rule out the possibility that some of the features in the spectra were a result of the PS I particle isolation procedure, rather than due to intact phylloquinone in its binding site. Here we will compare the (A1--A1) FTIR difference spectra obtained using static and time-resolved techniques, highlighting similarities and differences. We will also present a model for the A1 binding site in intact photosystem I.