Activation of Chlamydomonas rhodopsin in vivo does not require isomerization of retinal.
The unicellular eukaryote Chlamydomonas reinhardtii is a phototactic alga that swims toward or away from light, using rhodopsin as the photopigment. The activity of retinal analogues was tested in the mutant FN68, which has high phototactic sensitivity only after incubation with retinal or analogues of retinal. Analogues prevented from isomerizing about the 7-ene, 9-ene, 11-ene, 13-ene, or 15-ene (C = N+H) bonds retained full activity. Also, bleaching, protonation of the N, and a stable geometrically altered chromophore are not required for full activity. An attractive hypothesis is that charge redistribution in the excited state of retinal directly triggers the activity of rhodopsin.
Foster
K W
KW
Department of Physics, Syracuse University, New York 13244-1130.
Saranak
J
J
Derguini
F
F
Zarrilli
G R
GR
Johnson
R
R
Okabe
M
M
Nakanishi
K
K
D002696:Chlamydomonas / Q000378:metabolism*; D007202:Indicators and Reagents; D007536:Isomerism; D007700:Kinetics; D008027:Light; D015394:Molecular Structure; D012168:Retinal Pigments / Q000378:metabolism*; D012172:Retinaldehyde / Q000031:analogs & derivatives / Q000138:chemical synthesis / Q000378:metabolism*; D012176:Retinoids / Q000378:metabolism*; D012243:Rhodopsin / Q000378:metabolism*
D007202:Indicators and Reagents; D012168:Retinal Pigments; D012176:Retinoids; D012243:Rhodopsin; D012172:Retinaldehyde