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Structural Study
of Retinochrome Using Double Bond-Locked Analogue Chromophores.
Zheng, Xiang-Guo1
and Yoshihaya, Kazuo1
Suntory Institute for Bioorganic Research, Osaka 618-8503, Japan1
Abstract-
A variety of retinal analogues has been utilized to obtain information
of structure of the retinal proteins and also to investigate chromophore-retinal
protein interactions. Structural studies of retinochrome and rhodopsin
are useful for understanding the mechanism by which these retinal proteins
achieve such a high selectivity in the photoisomerization of the chromophore:
from all-trans to 11-cis in retinochrome while from 11-cis
to all-trans in rhodopsin. Photoreaction processes of retinochorme
have been studied mainly by UV-visible absorption spectroscopy. In this
study, three double bond-locked with five membered-ring retinal analogues,
all-trans-10,12-ethano- (1), 11,20-methano- (2),
and 12,14-ethano- (3) retinals were synthesized and incorporated
into retinochrome as the chromophores to investigate the effect of structural
changes in retinochrome. The 11,12-trans double bond locked aldehydes,
1 and 2, were smoothly incorporated into retinochrome
to afforded a pigments with  max
at 478 nm and 484 nm, respectively. Also 13,14-trans double bond
locked aldehyde 3 gave a pigment with 493 nm the max
at 369 nm. However completion of the pigments from 3 required
over 2days, whereas pigment formation from 1 and 2 finished
in 2h. Photoreaction of retinochrome 3 converted the all-trans
chromophore to the 11-cis-isomer while the 11-trans-locked
coromophore 1 and 2 were transfered to the 13-cis
isomers. The isomerization in retinochrome seems to have such a high
selectivity.
Keywords: Retinal
analogue, Retinochrome, Photoreaction
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