Movement of the ligand/receptor complex in rhodopsin (Rh) has been traced.
Bleaching of diazoketo rhodopsin (DK-Rh) containing 11-cis-3-diazo-4-oxo-re
tinal yields batho-, lumi-, meta-I-, and meta-II-Rh intermediates correspon
ding to those of native kh but at lower temperatures. Photoaffinity labelin
g of DK-Rh and these bleaching intermediates shows that the ionone ring cro
ss-links to tryptophan-265 on helix F in DK-Rh and batho-Rh, and to alanine
-169 on helix D in lumi-, meta-I-, and meta-II-Rh intermediates, It is like
ly that these movements involving a flip-over of the chromophoric ring trig
ger changes in cytoplasmic membrane loops resulting in heterotrimeric guani
ne nucleotide-binding protein (G protein) activation.