Spectral transitions in purple membranes from Halobacterium halobium. I. Effect of preliminary illumination on photochemical processes.

The effect of preliminary illumination of purple membranes by yellow light on the difference spectra of short-lived intermediates has been studied. It has been found that changes of the optical density of two of these intermediates, which have the maxima of the difference spectrum at 412 nm and 650 nm, coincides well with the kinetics off the known reversible transitions of the main band of the purple membrane absorption (560 570), i.e., 13-cis-trans transitions. The changes at 412 nm and 650 nm are proportional to the concentration changes of the all-trans retinal and 13-cis retinal, respectively. It was concluded that the formation of the short-lived 412 and 650 intermediates occurs in different photochemical cycles. The pH is found to affect the formation of the 650 intermediate.