EUGLENA-GRACILIS - IS THE PHOTORECEPTION ENIGMA SOLVED

Since the turn of the century the photosynthetic and photosensitive fl agellate Euglena gracilis has provided an elective point for photobiol ogical studies. Indeed, it plays a unique evolutionary role in photore ception, as its paraflagellar swelling can be considered as the first ciliary photoreceptor consisting of a natural three-dimensional crysta l of a membrane protein. Previous fluorescence and action spectra stud ies on the nature of the pigment content of this organelle suggested a flavin nature of its chromophores. Recently, theoretical consideratio ns, absorption microspectroscopic measurements, inhibition experiments on the biosynthesis of carotenoids, the photobehaviour in the presenc e of hydroxylamine hydrochloride, and the identification of all-trans- retinal by thin layer chromatography, high performance liquid chromato graphy (HPLC), absorption spectroscopy and gas chromatography-mass spe ctrometry (GC-MS) have indicated that rhodopsin is the photoreceptive molecule of this microorganism. All of these studies are compared and critically discussed on the basis of newly collected experimental data .