Spectral properties of Mastigocladus laminosus phycobilisomes embedded in poly(vinyl alcohol) films

Abstract

Polarized absorption, fluorescence and delayed time-resolved luminescence spectra were measured of phycobilisomes isolated from the cyanobacterium Mastigocladus laminosus and embedded in isotropic and anisotropic (stretched) poly(vinyl alcohol) (PVA) films. Stretching induced orientation of phycobilisomes and allowed differently oriented groups of chromophores to be photoselected by polarized light. From the set of polarized emission components, the anisotropy of fluorescence coefficients for the pools of differently oriented molecules was calculated. These coefficients are different in various regions of biliprotein emission. Contributions to emission anisotropy from pools of differently oriented chromophores are especially well resolved for a group of molecules oriented at large angles with respect to the PVA stretching axis. Polarized fluorescence spectra suggest strongly that more than one chain of pigment engaged in the energy transfer process is present in the investigated phycobilisomes. Delayed luminescence was observed in a region of prompt fluorescence and/or in the longer-wavelength region. Its intensity is about 10% of that of the prompt fluorescence. Decay times and yields of delayed luminescence excited in the phycoerythrocyanin (PEC) and C-phycocyanin (C-PC) absorption regions are different (τ PEC = 12 μs, τ C−PC = 38 μs). Delayed emission is probably, as for phycobilisomes without phycoerythrin, due to ionization of chromophores and delayed recombination.