The Journal of General Physiology, Vol 84, 49-62, Copyright © 1984 by The Rockefeller University Press
Metaretinochrome in membranes as an effective donor of 11-cis retinal for the synthesis of squid rhodopsin
T Seki
Aporetinochrome, which is a protein moiety of retinochrome without
chromophore retinal, is found in the membrane containing retinochrome. All
of the prosthetic retinal of retinochrome in membranes, which is all-trans
retinal, is bound to the chromophoric site on the protein moiety, with
protonated Schiff bases showing an absorption band with the maximum at 495
nm. On exposure to light, retinochrome is converted to metaretinochrome at
room temperature. The prosthetic retinals of metaretinochrome in membranes,
which are 11-cis retinals, are in two states: retinals bound to the
chromophoric site with protonated Schiff bases, and the free retinals,
which are separated from the protein moiety. These states are suggested
from the following observations. (a) The ratio of the absorbance at 470 nm
of metaretinochrome to that at 495 nm of the parental retinochrome differs
because of differences in samples and is higher in the purer preparations.
(b) The difference spectrum of absorption of metaretinochrome caused by
alkalinization shows two minimum peaks at approximately 420 and 470 nm. (c)
The rate of bleaching of metaretinochrome in membranes with dilute NH2OH is
much faster than that of retinochrome, and the absorption band in the near-
UV region is more susceptible to NH2OH than the visible absorption band.
The state of the prosthetic retinals in metaretinochrome was confirmed
directly by the reaction of metaretinochrome in membranes with NaBH4. After
treatment with NaBH4, the sodium dodecyl sulfate- polyacrylamide gel
electrophoretic pattern shows two fluorescent bands: one at the position
that corresponds to the retinochrome protein (mol wt 27,000 +/- 2,000), and
another at the front of migration, where no band of protein is observed.
Retinoids extracted from the NaBH4-treated metaretinochrome in membranes
and analyzed with high-pressure liquid chromatography show a main peak of
11-cis retinol. The results of this and earlier (Seki et al., 1982) papers
are summarized, and it is strongly suggested that metaretinochrome in the
squid retina may play the role of 11-cis retinal donor for opsin and
contribute to the synthesis of the squid rhodopsin.
CiteULike 
Complore 
Connotea 
Del.icio.us 
Digg 
Reddit 
Technorati What's this?
