title: Initial spectroscopic characterization of the ciliate photoreceptor stentorin.
abstract: Stentorin serves as the primary photosensor in the single cell ciliate, Stentor coeruleus, for its photophobic and phototactic response to light of visible wavelengths. We separated two subunits, stentorin-2A and -2B, from the previous stentorin complex ('stentorin-2') of greater than half a million molecular mass isolated from the photoreceptor organelle (pigment granule). Stentorin-2B bears the chromophore covalently linked to an approx. 50 kDa apoprotein, as determined by SDS-urea-PAGE. Partial amino acid sequences were obtained from this 50 kDa subunit. Its visible and CD spectra were found to be similar to those of stentorin-2. The steady-state and time-resolved fluorescence spectra of stentorin-2B, in H2O and D2O buffers, were also similar to those of stentorin-2. This suggests that the 50 kDa subunit retains the spectral integrity and primary photoreactivity of the stentorin-complex. The picosecond time-resolved fluorescence study revealed that the short picosecond emission component (tau F approximately equal to 8-10 ps) was the predominant emitting species in stentorin-2B and -2, followed by longer decaying species. No deuterium solvent effect was seen in this fast-decaying species. The possible mechanism for the primary photoreaction appears to involve electron transfer coupled with proton transfer.
authors.affiliation: Department of Chemistry, University of Nebraska, Lincoln 68588-0304, USA.
authors.forename: R
authors.initials: R
authors.lastname: Dai
authors.forename: T
authors.initials: T
authors.lastname: Yamazaki
authors.forename: I
authors.initials: I
authors.lastname: Yamazaki
authors.forename: P S
authors.initials: PS
authors.lastname: Song
mesh_terms: D000596:Amino Acids / Q000032:analysis; D000818:Animals; D056890:Eukaryota / Q000737:chemistry*; D017956:Photoreceptor Cells, Invertebrate / Q000737:chemistry*; D011083:Polycyclic Compounds / Q000737:chemistry*; D013050:Spectrometry, Fluorescence
chemical_list: D000596:Amino Acids; D011083:Polycyclic Compounds; C021252:stentorin I; C021253:stentorin II