Photosensory transduction in unicellular eukaryote Blepharisma.
In the ciliated protozoan Blepharisma, step-up photophobic response is mediated by a novel type of photosensory complex of pink-colored pigment "blepharismins" and 200-kDa membrane protein contained in the pigment granules located just beneath the plasma membrane. We found that the fluorescence intensity of isolated blepharismins decreased prominently with a decrease of H(+) concentration in the surrounding medium. In the present study, therefore, we utilized the endogenous pigment blepharismins as the pH indicator. Light stimulation evoked a sudden decrease in fluorescence intensity in a photosensitive anterior portion of the cell, suggesting that a drop in H(+) concentration occurred in the anterior region. The result indicates that the photosignal is transduced into cytoplasmic signaling of H(+) translocation across the outer membrane surrounding the pigment granules, so that cytosolic H(+) concentration in the vicinity of plasma membrane might be increased.
Matsuoka
T
T
Department of Biology, Kochi University, Kochi 780-8520, Japan. tmatsuok@cc.kochi-u.ac.jp
Kotsuki
H
H
D000818:Animals; D016798:Ciliophora / Q000737:chemistry / Q000502:physiology*; D006863:Hydrogen-Ion Concentration; D007091:Image Processing, Computer-Assisted; D008027:Light; D008565:Membrane Proteins / Q000737:chemistry; D010569:Perylene / Q000031:analogs & derivatives* / Q000737:chemistry*; D015398:Signal Transduction / Q000502:physiology*; D013050:Spectrometry, Fluorescence
D008565:Membrane Proteins; C092293:blepharismin; D010569:Perylene