IDENTIFICATION OF A NEW INTERMEDIATE STATE THAT BINDS BUT NOT ACTIVATES TRANSDUCIN IN THE BLEACHING PROCESS OF BOVINE RHODOPSIN

Using time-resolved low-temperature spectroscopy, we have examined whe ther or not bovine rhodopsin has a unique transducin-binding state, me ta I-b, previously detected from chicken rhodopsin, Unlike chicken met a I-b, bovine meta I-b was detected only by detailed kinetics analysis of the bleaching process, but it was stabilized by transducin and vis ualized in the observed spectral changes, From the effect of GTP gamma S, it was revealed that meta I-b induced no GDP-GTP exchange reaction in transducin. Thus meta I-b is a common intermediate of vertebrate r hodopsin and transducin is activated in tao steps by meta I-b and meta II. (C) 1998 Federation of European Biochemical Societies.