PICOSECOND TIME RESOLVED ENERGY TRANSFER IN ISOLATED PHYCOBILISOMES FROM RHODELLA VIOLACEA (RHODOPHYCEAE) *

Energy‐transfer kinetics in isolated phycobilisomes (PBS) of the red alga Rhodella violacea have been measured by detecting both ground state recovery and fluorescene rise or decay using a synchronously pumped cavity‐dumped dye laser as excitation source. For the first time the constituent phycobiliproteins of PBS have been excited selectively, thus allowing the kinetics of both directly and indirectly excited pigments to be followed. Energy‐transfer between the phyeobiliproteins, which was found to proceed extremely fast, is governed by nonexponential kinetics at low excitation intensities. When analyzed in a biexponential model, the main components of the fluorescence of B‐phycoerythrin (B‐PE) and C‐phycocyanin (C‐PC) decay with τ= 34 ps and τ= 25 ps, respectively. Evidence is presented that transfer between the biliprotein pigments is close to a single‐step process with some contribution of homotransfer. Fluorescence quantum yields of PBS have been determined as a function of the excitation wavelength and were found to reflect a dissociation equilibrium involving ca. 10% dissociated PBS at the concentrations studied.