The Eyes Have It

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Science  27 Jun 2003:
Vol. 300, Issue 5628, pp. 2007
DOI: 10.1126/science.300.5628.2007b

Congenital night blindness (CNB) occurs when retinal rod photoreceptor cells are inappropriately stimulated so that their sensitivity to dim light is reduced. Three rhodopsin mutants are known to cause CNB in humans, but it has been unclear whether desensitization is caused by constitutive activation of the apoprotein (opsin) or activation of the holoprotein by thermal isomerization of the 11-cis-retinal chromophore to all-trans retinal. Jin et al. resolved this by isolating photoreceptor cells containing each of the three rhodopsin mutants from transgenic frogs, and measuring their photoresponse before and after incubation with 11-cis-retinal. Intensity response curves and dim flash kinetics showed that all mutants were desensitized initially but recovered wild-type photoresponses after incubation with 11-cis-retinal. The addition of 11-cis-retinal would not be expected to have any effect on active rhodopsin; however, it could convert active opsin to inactive rhodopsin. Thus it appears that rhodopsin mutations cause CNB by constitutively activating opsin and not by increasing thermal isomerization of the retinal chromophore.—VV

Nature Neurosci. 10.1038/nn1070 (2003).

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