We have demonstrated that photosensor controlling photobehavior of unicellular organism Blepharisma japonicum is a quinone/200 kD protein complex which is quite different from rhodopsin. The present study aimed to reveal the structure and function of quinone photoreceptor as described follows.
1.Three-dimensional structure of quinone pigment : Three-dimensional structue of quinone was calculated and suggested by using MOPAC (PM3). We have tried to obtain crystal of pigment for crystal structure analysis. 2.Localization of quinone pigment : The molecular structure of 5 types of quinone (BL-1,2,3,4,5) contained in Blepharisma cells was determined, and photo-sensitive region of cell body was demonstrated to contain only BL-2. Therefore, it is concluded that BL-2 is a primary photosensor for the photoresponse. 3.Isolation of DNA encoding 200kD protein : The partial amino acid sequence of 200 kD protein was determined. This sequence has a large homology with that of a certain kind of H^+ transporting protein. Oligonucleotide was synthesized and cloning of DNA encoding 200 kD protein was tried by PCR.However, we failed to obtain cDNA clone, because quinone pigment contained in the cells inhibited PCR.4.Phototransduction : Fluorescence analysis using pH indicator revealed that photo-signal might transduced into local changes in H^+ concentration in the cell or pigment granules.