Color discrimination in halobacteria: spectroscopic characterization of a second sensory receptor covering the blue-green region of the spectrum.
Proc Natl Acad Sci U S A
; 83(19): 7272-6, 1986 Oct.
Article
em En
| MEDLINE
| ID: mdl-3463965
ABSTRACT
Halobacterium halobium is attracted by green and red light and repelled by blue-green and shorter wavelength light. a photochromic, rhodopsin-like protein in the cell membrane, sensory rhodopsin sR587, has been identified as the receptor for the long-wavelength and near-UV stimuli. Discrepancies between the action spectrum for the repellent effect of blue light and the absorption spectrum of sR587 and its photocycle intermediate S373 strongly suggest the existence of an additional photoreceptor for the blue region of the spectrum. Transient light-induced absorbance changes in intact cells and cell membranes show, in addition to sR587, the presence of a second photoactive pigment with maximal absorption near 480 nm. It undergoes a cyclic photoreaction with a half-time of 150 msec. One intermediate state with maximal absorption near 360 nm has been resolved. The spectral properties of the new pigment are consistent with a function as the postulated photoreceptor for the repellent effect of blue light. The phototactic reactions and both pigments are absent when retinal synthesis is blocked; both can be restored by the addition of retinal. These results confirm and extend similar observations by Takahashi et al. [Takahashi, T., Tomioka, H., Kamo, N. & Kobatake, Y. (1985) FEMS Microbiol. Lett. 28, 161-164]. The archaeobacterium H. halobium thus uses two different mechanisms for color discrimination; it uses two rhodopsin-like receptors with different spectral sensitivities and also the photochromicity of at least one of these receptors to distinguish between three regions covering the visible and near-UV spectrum.
Texto completo:
1
Coleções:
01-internacional
Base de dados:
MEDLINE
Assunto principal:
Células Fotorreceptoras
/
Retinoides
/
Bacteriorodopsinas
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Halobacterium
Tipo de estudo:
Prognostic_studies
Idioma:
En
Revista:
Proc Natl Acad Sci U S A
Ano de publicação:
1986
Tipo de documento:
Article