PHOTOACTIVATED CONFORMATIONAL-CHANGES IN RHODOPSIN - A TIME-RESOLVED SPIN-LABEL STUDY

Rhodopsin has been selectively spin-labeled near the cytoplasmic termi ni of helices C and G. Photoactivation with a light flash induces an e lectron paramagnetic resonance spectral change in the millisecond time domain, coincident with the appearance of the active metarhodopsin II intermediate. The spectral change is consistent with a small movement near the cytoplasmic termination of the C helix and reverses upon for mation of the MIII state. These results provide an important link betw een the optical changes associated with the retinal chromophore and pr otein conformational states.