CHIMERIC PHOTORECEPTOR SYSTEM FROM VERTEB RATE RETINA - IN-VITRO SUBSTITUTION OF RHODOPSIN BY PHOTOSENSITIVE PIGMENT FROM UNICELLULAR ALGA CHLAMYDOMONAS-REINHARDTII

It has been confirmed that in the vertebrate photoreceptor system stim ulating 3', 5'-cGMP phosphodiesterase in vitro rhodopsin can be succes sfully replaced by photosensitive pigment contained in the eyespots of the unicellular green alga Chlamydomonas reinhardtii. The same effect has been found with the eyespots from mutant alga cells (without caro tinoids containing opsin-like protein) but only after their preincubat ion with 11-cis- or all- trans-retinals. But in the latter case the ex tent of photostimulated enzyme activation did not depend on the presen ce of Gpp(NH)p in the incubation medium, being the same with and witho ut nucleotide. The eyespots of the mutant cells preincubated with both retinal isomers (unlike to the eyespots which were not preincubated) induced photostimulation of transducin GTP-ase but the extent of enzym e activation was considerably lower than that in the presence of rhodo psin. Five proteins which bind all-trans retinal have been found in th e eyespot fraction, with two of them (M(r) 21000 and 30000) predominan tly binding atl-trans-retinal. The 30 kDa protein can also bind 11-cis -retinal.