Substitution of retinal by analogs in retinal pigments of halobacterium halobium contribution of bacterio rhod opsin and halo rhod opsin to photo sensory activity
Schimz, A.; Sperling, W.; Ermann, P.; Bestmann, H.J.; Hilderbrand, E.
Photochemistry and Photobiology 38(4): 417-424
1983
ISSN/ISBN: 0031-8655
Accession: 006536049
In H. halobium, retinal is the chromophore of the light-energy coverting pigments bacteriorhodopsin (BR) and halorhodopsin (HR) and of the sensory photosystems, PS 370 and PS 565. In both photosystems and in BR and HR, retinal was substituted by retinal analogs. Retinal2 (3,4-dehydro-retinal) shifts the main sensitivity maximum of PS 370 and of PS 565 by .apprx. 15 nm to longer wavelengths. The absorption maxima of BR and HR are shifted in the same direction, but by 32 nm. 13-Ethylretinal and 13-propylretinal shift the main sensitivity maximum of each sensory photosystem to shorter wavelengths; the absorption maxima of BR and HR are shifted in the same direction but to a smaller extent. Both sensory photosystems are equally active with retinal and with each of the 3 analogs as the chromophore. After substitution of retinal by the analogs, the action spectra of PS 565 of the BR-containing strain R1L3 show a secondary sensitivity peak in addition to the main peak. This secondary peak matches the absorption maximum of the corresponding BR. In the action spectra of the BR-deficient strain ET-15, this secondary peak is missing. Action spectra of PS 565 of the BR-deficient strain L-33, which synthesizes increased amounts of HR, with all retinals show a secondary peak which matches the absorption maximum of the corresponding HR. The analogs can substitute retinal in both sensory pigments and in BR and HR. The data support the previous assumption that both BR and HR, although not required for photosensory activity, can contribute to photosensing through PS 565.