Journal of Fluorescence, Vol. 11, No. 1, 2001 Spectral Properties of Bacteriochlorophyll c in Organisms and in Model Systems Jacek Goc, 1 Alina Dudkowiak, 1 Zygmunt Gryczyn ´ ski, 2 Ignacy Gryczyn ´ ski, 2 Bogumil Zelent, 2 and Danuta Fra ˛ckowiak 1,3 Received July 28, 2000; revised December 18, 2000; accepted December 22, 2000 Polarized absorption and fluorescence spectra of bacteriochlorophyll c and green photosynthetic bacterium Prostheecochloris aestuarii cells and cell fragments embedded in stretched polymer film were measured. In pigment samples the artificial oligomers of bacteriochlorophyll c (with absorption about 750 nm) and other forms of this pigment and bacteriopheophytin (with absorption at 670 nm) were present. In bacteria samples, embedded in polymer, oligomers were in high degree disaggregated and as a result the absorption about 670 nm was observed. Previously for similar sets of samples the decay of fluorescence excited only at one wavelength was analyzed on three exponential components, but exact lifetime values of these components for various samples were different. The aim of present paper was to check if these differences occur because of various contributions to decay from three well defined forms or if they were related to the existence of several pigment forms with slightly different lifetimes. The global analysis of data obtained for various excitation and observation wavelengths of fluorescence were done. From this analysis it follows that the second situation occurs. For a model system containing artificial oligomers the largest component of decay has a  4 of about 0.183 ns or 0.136 ns depending on observation wavelength. For the bacteria sample, in which the emission at 680 nm is the superposition from various pigments, global analysis done for various excitation wavelengths shows also that the  values differ depending on the regions of fluorescence observation. From polarized spectra, it follows that in the model system the pigments absorbing at 670 nm are randomly distributed whereas oligomers are highly oriented. In bacteria fragments absorbing at 670 nm pigment molecules can be divided into two groups: one oriented along the axis of film stretching and the second practically randomly distributed. In living organisms, under some conditions, small amount of 670 nm pigments can be present and can work as excitation energy traps or as antenna transferring the excitation. Present results show that the role of various pools of 670 nm absorbing pigments can be different because of their differing orientation. KEY WORDS: Bacteriochlorophyll c; green bacteria; lifetime of fluorescence; oligomers of bacteriochlorophyll c; polarized spectroscopy; polymer films. INTRODUCTION information about the location of absorption and fluores- cence transition moments (TMs) 4 in a frame of molecule as well as about the influence of local electric fields It is known, that from polarized absorption and fluo- and interactions with surroundings on pigment spectral rescence spectra of oriented dyes it is possible to draw 3 To whom correspondence should be addressed. Fax: +48 +61 6652324. E-mail: frackow@phys.put.poznan.pl 1 Institute of Physics, Poznan ´ University of Technology, Nieszawska 13, 60 965 Poznan ´, Poland. 4 Abbreviations used: absorption anisotropy (s): bacteriochlorophyll (BChl): bacteriopheophytin (BPhe); dichroic ratio (R 2 ); lifetime (); 2 Center for Fluorescence Spectroscopy, University of Maryland, School of Medicine, Department of Biochemistry and Molecular Biology, polyvinyl alcohol (PVA); Fenna–Mathews–Olson complexes (FMO); transition moments (TMs). 725 West Lombart Street, Baltimore, Maryland 21201. 53 1053-0509/01/0300-0053$19.50/0  2001 Plenum Publishing Corporation