Previous studies of constitutively activated mutants of opsin in the absence of chromophore were carried out in crude cell membranes because such mutants could not be recovered in a detergent-solubilized form in the active state We employed a strategy in which a stabilizing disulfide bond allowed for successful purification of a constitutively activated mutant opsin N2C/E113Q/M257Y/D282C solubilized in nonionic detergent from mammalian cell culture The purified mutant opsin is able to activate transducin to a higher degree than opsin and may prove useful for future structural studies of the active state of GPCRs (C) 2010 Elsevier Inc All rights reserved