Fourier Transform Infrared Studies of the Secondary Electron Acceptor, A1

Abstract

Fourier transform IR (FTIR) difference spectroscopy is a useful tool for the study of the structural details of electron transfer cofactors (and their binding sites) in photosynthetic complexes. To date, most FTIR difference spectroscopic studies of photosynthetic complexes have been static expts. in the sense that a steady-state population of an excited state species is photo-accumulated. In intact Photosystem I (PS I) particles the P700+A-1 state is short-lived, and not easily studied using static FTIR difference techniques. Time-resolved techniques are required. In this article the use of time-resolved step-scan FTIR difference spectroscopy for the study of the P700+A-1 state in intact PS I particles from cyanobacteria is described. With reliable P700+A-1 FTIR difference spectra it is possible to construct A-1/A1 FTIR difference spectra. The main obstacle to obtaining reliable A-1/A1 FTIR difference spectra is the sensitivity of the time-resolved step-scan FTIR approach. Until now, no A-1/A1 FTIR difference spectra have been obtained using intact PS I particles. In this article, recent work in our lab is described where we have used low-temp. (77 K), time-resolved step-scan FTIR difference spectroscopy to generate A-1/A1 FTIR difference spectra for intact cyanobacterial PS I particles that are unlabeled, deuterated, 15N, and 13C labeled. From a consideration of the isotope-induced band-shifts, assignments for specific bands in the difference spectra are proposed. [on SciFinder (R)]