Light‐induced Conformational Changes in Cattle Rhodopsin as Probed by Measurements of the Intefface Potential

A novel technique of capacitative coupling of oriented rhodopsin at a polar/apolar interface allows the time resolved investigation of conformational changes following a flash. Electric signals arise as a consequence of changes of the interface potential. A signal occurring within milliseconds behaves like the R2‐phase of the “early receptor potential” (= ERP). This response is interpreted as a conformational change of rhodopsin. No correlation of this signal is found to the spectroscopically defined metarhodopsin I‐metarhodopsin II transition. The temperature dependence of the conformational change coincides with the temperature dependence of the latency of the ‘a‐wave’ of the electroretinogram, reported by Arden and Ikeda (1968). It is suggested that the command step of visual excitation is the conformational change and not one of the spectroscopically defined photolysis steps of rhodopsin. Analysis of slower electrical signals following the fast response is in accordance with the model of a light‐induced pore formation.