Effect of chloride ion on the thermal decay process of the batho intermediate of iodopsin at low temperature.
The photochemical and the subsequent thermal behaviors of iodopsin (Cl(-)-bound form) and N-iodopsin (iodopsin whose Cl- was replaced by NO3-) in CHAPS-phosphatidylcholine (PC) were studied by low-temperature spectrophotometry. Irradiation of the iodopsin preparation at -185 degrees C produced a photo-steady-state mixture composed of iodopsin, bathoiodopsin, and isoiodopsin. Bathoiodopsin was thermally reverted to the original iodopsin. These results were almost the same as those reported previously [Yoshizawa, T., & Wald, G. (1967) Nature 214, 566-571] in which iodopsin was extracted with 2% digitonin. Therefore, photochemical and subsequent thermal behaviors of iodopsin were independent of the detergent to solubilize iodopsin. Irradiation of N-iodopsin at -185 degrees C produced the similar photo-steady-state mixture. However, N-bathoiodopsin was thermally converted to the next intermediate, presumably N-lumiiodopsin. These results suggest that the batho-lumi transition of iodopsin at low temperature is likely to be inhibited by the Cl- bound to the protein moiety of iodopsin, while at room temperature the Cl- bound to iodopsin could be released on the conversion process of batho- to lumiiodopsin.
Imamoto
Y
Y
Department of Biophysics, Faculty of Science, Kyoto University, Japan.
Kandori
H
H
Okano
T
T
Fukada
Y
Y
Shichida
Y
Y
Yoshizawa
T
T
D000818:Animals; D002645:Chickens; D002712:Chlorides / Q000378:metabolism*; D008027:Light; D012168:Retinal Pigments / Q000378:metabolism*; D017299:Rod Opsins; D013057:Spectrum Analysis; D013696:Temperature; D013816:Thermodynamics
D002712:Chlorides; D012168:Retinal Pigments; D017299:Rod Opsins; C034941:iodopsin