Analyses of structure of photoreceptor organelle and blepharismin-associated protein in unicellular eukaryote Blepharisma

In the ciliated protozoan Blepharisma, step-up photophobic response Is beli eved to be mediated by a novel type of photosensory pigment known as "bleph arismins" (BL) that are contained in the pigment granules located just bene ath the plasma membrane, We examined the ultrastructure of the pigment gran ules by freeze-fracture and thin-section electron microscopy and proposed a schematic diagram showing the granules' three-dimensional inner membranous structure. Some of the BL are suggested to be associated with 200 kDa memb rane protein, High-pressure liquid chromatography analysis of pigment speci es associated with 200 kDa protein obtained from blue forms of Blepkarisma (oxyblepharisma) revealed that the 200 kDa protein was associated with five types of oxyblepharismin. The fluorescence intensity was increased when th e pigments were dissociated from the 200 kDa protein, The result supports t he hypothesis that the pigment-200 kDa complex is able to transduce light e nergy Into signals mediating the photobehavior of Blepharisma.