POLARIZED TIME‐RESOLVED FLUORESCENCE SPECTRA OF PHYCOBILISOMES ISOLATED FROM Tolypothrix tenuis EMBEDDED IN POLY(VINYL ALCOHOL) FILM

Abstract

Time-resolved fluorescence spectra in the ps tiine range were measured on phycohilisome (PBS) emhedded in poly(viny1 alcohol) films. The cyanohacteriutn To!\.porhri.u renuis was used :I> a source of PBS because the pigment composition and the structure o f the PBS are well defined. Isotropic PBS in the unstretched film and PBS uniaxially oriented in the stretched film were investigated. Diameters of PBS heinidiscs were oriented parallel t o the film-stretching direction. The timeresolved fluorescence spectra of the unstretched sample and of the two polarized componcnts in the stretched samples showed several differences in the rise and decay. The delay time. estimated from the time span between the maximum laser pulse and maximal intensity of the phycocyanin and allophycocyanin fluorescence, was much longer than that reported in the aqueous media. This suggests occurrence of a higher thermal deactivation of PBS in polymer film than in aqueous media. The excitation energy transfer from excited phycocrythrin to allophycocyanin was more efficient in the unstretched than in the stretched samples, and it was greater in the parallel polarized component o f the stretched sample than in the perpendicular component. The present results are in agreement with a previous suggestion which states that there are two independent pathways of excitation energy transfer in PBS and that there is more than one final emitter of fluorescence. The molecules taking part in various pathways of energy transfer differ in their orientation within PBS.

Fluorescence Polarization Studies of B‐Phycoerythrin Oriented in Polymer Film¶

“…Complex shapes of fluorescence and fluorescence excitation spectra and different decay of fluorescence parameters show that in B‐PE chains of excitation, donors and acceptors are present, similar chemically but differently ordered and differently transferring excitation forms of PEB. The formal division of chromophores into groups: s (sensitizing), m (medium) and f (fluorescent) (15) seems to be oversimplified.…”

Interactions between photosynthetic pigments in organisms and in model systems

“…Such models have been investigated (Frąckowiak et al 1969) in order to establish the spectral properties of pigments occurring in various organisms . Several types of anisotropic models for the investigations of the pigments (Martyński et al 1998) or for the measurements of the parts of photosynthetic systems or even of the whole small organisms have been used: stretched polymers (Frąckowiak et al 1989, Ptak et al 1996, liquid crystal cells (Kowalczyk et al 1996b), or various mono-and multi-Langmuir-Bloodget layers . For every sample a proper type of anisotropic matrix has to be selected.…”

“…Using polarized light PAS (Frąckowiak et al 1985, 1989, Frąckowiak and Ptak 1994 it is possible to establish which element of complex biological sample is responsible for measured heat (Frąckowiak et al 1996). Before the application of spectral methods to whole organisms or their large parts it is convenient to apply similar methods to studying simpler model systems having known structure.…”