COMBINED OPTICAL AND PHOTOELECTRIC STUDY OF THE PHOTOCYCLE OF 13-CIS BACTERIORHODOPSIN

The photocycle of the 13-cis retinal containing bacteriorhodopsin was studied by three different techniques. The optical multichannel analyz er monitored the spectral changes during the photocycle and gave infor mation about the number and the spectrum of the intermediates. The abs orption kinetic measurements provided the possibility of following the absorbance changes at several characteristic wavelengths. The electri c signal provided information about the charge motions during the phot ocycle. The results reveal the existence of two intermediates in the 1 3-cis photocycle, one with a short lifetime having an average of 1.7 m u s and an absorption maximum at 620 nm. The other, a long-living inte rmediate, has a lifetime of about 50 ms and an absorption maximum arou nd 585 nm. The data analysis suggests that these intermediates are in two parallel branches of the photocycle, and branching from the interm ediate with the shorter lifetime might be responsible for the light-ad aptation process.