Analysis of time-resolved emission spectra of oriented phycobilisomes

Abstract

The polarized time-resolved (in ps range) fluorescence spectra of phycobilisomes obtained from cyanobacteria Tolypothrix tenuis embedded in poly(vinyl alcohol) films and oriented by film stretching have been analysed. Fluorescence spectra were deconvoluted on Gaussian components supposing the same positions of components maxima in three sets of time-resolved spectra taken in natural and polarized light. A good fit of the experimental and calculated spectra was obtained when using the following maxima: 580 and 595 nm in the phycoerythrin region, 634 and 650 nm in the phycocyanin region, 660 and 680 nm in the allophycocyanin region. The area under curve of the Gaussian component vs. time gives the shape of rise and decay of emission of chromophores contributing to the given component. These kinetics were analysed using several model functions. The experimental excitation profile was convoluted with a multiexponential model individually or “globally” e.g. assuming the same lifetime values for the given species in all sets of spectra. The Foerster-Hauser types of two- and three-dimensional models we also convoluted with excitation profile and fitted to the decay of primarily excited species. The first acceptor decay can be described well by the Foerster-Hauser models or by a monoexponential function. The accuracy of fit in either case of three- and two-dimensional Foerster-Hauser function is similar. The fluorescence rise and decay of the next species in a donor-acceptor chain can be analysed in terms of two or three exponential functions. Obtained lifetimes of fluorescence are similar to those reported in literature. The results suggest that there are more than one chain of excitation donors and acceptors in the phycobilisomes of cyanobacteria Tolypothrix tenuis.