A friend writes to tell me that this article uses the design concept effectively. What do you think?
ASAP Biochemistry, ASAP Article, 10.1021/bi800357b
Web Release Date: June 19, 2008
Copyright © 2008 American Chemical Society
11-cis- and All-trans-Retinols Can Activate Rod Opsin: Rational Design of the Visual Cycle†
Masahiro Kono,* Patrice W. Goletz, and Rosalie K. Crouch
Department of Ophthalmology, Medical University of South Carolina, Charleston, South Carolina 29425
Received February 29, 2008
Revised Manuscript Received May 25, 2008
Rhodopsin is the photosensitive pigment in the rod photoreceptor cell. Upon absorption of a photon, the covalently bound 11-cis-retinal isomerizes to the all-trans form, enabling rhodopsin to activate transducin, its G protein. All-trans-retinal is then released from the protein and reduced to all-trans-retinol. It is subsequently transported to the retinal pigment epithelium where it is converted to 11-cis-retinol and oxidized to 11-cis-retinal before it is transported back to the photoreceptor to regenerate rhodopsin and complete the visual cycle. In this study, we have measured the effects of all-trans- and 11-cis-retinals and -retinols on the opsin’s ability to activate transducin to ascertain their potentials for activating the signaling cascade. Only 11-cis-retinal acts as an inverse agonist to the opsin. All-trans-retinal, all-trans-retinol, and 11-cis-retinol are all agonists with all-trans-retinal being the most potent agonist and all-trans-retinol being the least potent. Taken as a whole, our study is consistent with the hypothesis that the steps in the visual cycle are optimized such that the rod can serve as a highly sensitive dim light receptor. All-trans-retinal is immediately reduced in the photoreceptor to prevent back reactions and to weaken its effectiveness as an agonist before it is transported out of the cell; oxidation of 11-cis-retinol occurs in the retinal pigment epithelium and not the rod photoreceptor cell because 11-cis-retinol can act as an agonist and activate the signaling cascade if it were to bind an opsin, effectively adapting the cell to light.
The rest of the article is in Paywall City. If you’re from there, read and spill.
Also, new at the Post-Darwinist:
Could life on Earth be much older than supposed?
Evolve already, huffingtons … the alligators are laughing at you
What happens when we assume there is no design in nature …
More on Louisiana’s “assault on Darwin” …
Darwin’s co-discoverer thought design can be detected in nature
History moment: Quick, relabel that exhibit!
“Accepting evolution” does not make you an atheist… oh, puh-LEASE! Not this rubbish again!