Relationships between the change in threshold of the fast PIII response and the rhodopsin photoproduct content were studied in the isolated bullfrog retina treated with Ba2+ and aspartate. A reduction in the extracellular Ca2+ concentration from 1.0 to 0.01 mM caused an increase in the decay rate of 380 nm absorbing photoproducts (metarhodopsin II and retinal) and metarhodopsin III. In both nor...

Opsin, the rhodopsin apoprotein, was recently shown to be an ATP-independent flippase (or scramblase) that equilibrates phospholipids across photoreceptor disc membranes in mammalian retina, a process required for disc homoeostasis. Here we show that scrambling is a constitutive activity of rhodopsin, distinct from its light-sensing function. Upon reconstitution into vesicles, discrete conforma...

Activation of the visual pigment rhodopsin is caused by 11-cis to -trans isomerization of its retinal chromophore. High-resolution solid-state NMR measurements on both rhodopsin and the metarhodopsin II intermediate show how retinal isomerization disrupts helix interactions that lock the receptor off in the dark. We made 2D dipolar-assisted rotational resonance NMR measurements between (13)C-la...

Most of the photoreceptors of the fly compound eye have high sensitivity in the ultraviolet (UV) as well as in the visible spectral range. This UV sensitivity arises from a photostable pigment that acts as a sensitizer for rhodopsin. Because the sensitizing pigment cannot be bleached, the classical determination of the photosensitivity spectrum from measurements of the difference spectrum of th...

Rhodopsin is a 7-helix, integral membrane protein found in the rod outer segments, which serves as the light receptor in vision. Light absorption by the retinylidene chromophore of rhodopsin triggers an 11-cis-->all-trans isomerization, followed by a series of protein conformational changes, which culminate in the binding and activation of the G-protein transducin by the metarhodopsin II (Meta ...

The equilibria between metarhodopsins I and II (MI and MII) and the binding of MII to retinal G protein (G) were investigated, using the dual wavelength absorbance response of rod disk membrane (RDM) suspensions to a series of small bleaches, together with a nonlinear least-squares fitting procedure that decouples the two reactions. This method has been subjected to a variety of theoretical and...