Transient spectra of intermediates in the photolytic sequence of octopus rhodopsin.

The intermediate photolytic sequence of octopus rhodopsin was studied at different temperatures and different pH values by means of a flash photolysis-rapid scan spectrophotometry near physiological temperature. The first photoproduct in the photolysis of rhodopsin was lumirhodopsin. Transformation of lumirhodopsin leads to mesorhodopsin took place independently of the pH of the solution. Mesorhodopsin was transformed to acid metarhodopsin in acid solution. In alkaline solution, mesorhodopsin was transformed to transient acid metarhodopsin whose absorption spectrum was similar to acid metarhodopsin. Transient acid metarhodopsin was then transformed to alkaline metarhodopsin reaching a tautomeric equilibrium which was determined by the pH of the solution.