Triplet-Minus-Singlet Optical Difference Spectroscopy of Some Green Photosynthetic Bacteria

Abstract

Several pigment—protein complexes have been isolated (H. VasmeL et aL.,1983, 1984) ta wit: 1) the core compLex ([[}J 2) the photosys.tem—pigment complex (PP), 3) the reaction—center—pigment protein complex (RCPP), 4) the Light—harvesting water—soluble antennai complex (LHP). The RCPP complex contains the reaction center (RC), the core complex and SUbunits of LHP J all membrane—bound; the PP complex contains in addition two loosely bound LHP molecules. The CC is not photoactive. We summarize triplet data obtained by absorbance—detected magnet ic resonance (RDMR) at 1.12 K, and present ROMR—monitored triplet—minus—singlet spectra of these four complexes.

The RCPP complex contains three triplet states, one characteristic of P840T , one identical to that of the core complex and one similar to that of isolated LHP. The triplet—minus—singlet (T — 5) spectra of the complexes were measured using RDMR. This allows one to discriminate between T — 5 spectra of the various triplet states when present in one complex by selecting the appropriate microwave transition frequency. The T — S spectra of PP, Repp and CC complexes are shown in Figs. 1 and 2. The corresponding linear dichroic CLD—CT — S)} spectra of P840T are shown in Fig .. 3.