Fast excited-state reaction in the photoreceptor pigment-protein complex of the ciliate Blepharisma japonicum

The primary phototransduction steps of the protozoan Blepharisma japonicum's light perception were studied by subpicosecond transient absorption spectroscopy. The free chromophore of the ligbt-adapted cell, oxyblepharismin, was characterized in solution and compared to the pigment-protein complex. Although showing similar steady-state and transient spectra, oxyblepharismin and its protein complex display noticeably different excited-state dynamics. In the chromoprotein, a pronounced fast biexponential decay (5 ps and 60 ps) is observed, which is not found in the corresponding kinetics of the isolated pigment. This early behavior could be the signature of a specific primary phototransduction process.