Energy Storage in the Primary Photoreaction of Bovine Rhodopsin. A Photoacoustic Study

Photoacoustic spectroscopy is used to investigate the uptake of energy in the primary photoreaction of bovine visual pigment (Rhodopsin → Bathorhodopsin). It is shown that very concentrated dried rod outer segment membranes have a sufficient thermal diffusivity to be analyzed by this technique. From the photoacoustic and absorption spectra of these membranes, the low temperature dissipation spectrum has been obtained and the results are consistent with the storage of 145 kJ mol‐1 in the primary event of vision having a quantum yield of 0.67. By photoacoustic spectroscopy, this process is continuously monitored from 350 to 550 nm and its efficiency is found to vary by less than 10%, even in the spectral region of the β‐band of rhodopsin.