Thermal recovery of iodopsin from its meta I‐intermediate

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Abstract
The thermal reaction of meta I‐intermediate of iodopsin (metaiodopsin I), a chicken red‐sensitive cone pigment, was studied by low‐temperature spectrophotometry at −20°C. Irradiation of iodopsin at −20°C produced metaiodopsin I, whose absorption maximum was at about 470 nm. An incubation of metaiodopsin I at −20 °C resulted in a conversion to metaiodopsin II having absorption maximum at about 380 nm, as well as a concurrent formation of a red‐shifted product stable at room temperature. Since the absorption spectrum and photo‐reactivity of the red‐shifted product were identical with those of iodopsin, the red‐shifted product should be iodopsin. Thus a part of metaiodopsin I can revert to iodopsin by the thermal reaction unlike metarhodopsin I.