The all-trans-retinal of the native chromoprotein of bacteriorhodopsin
(BR) purple membrane was replaced with the synthetic 4-keto retinal.
Gelatin films were made from the reconstituted BR and the intensity-de
pendent basic optical properties were investigated. It is shown that a
t room temperature the M-state is composed of two different absorption
bands (maximum at 413 nm and 435 nm) with different relaxation times.
Unexpected low-intensity transmission properties which cannot be expl
ained by the two-level model are reported. The M-state of the 4-keto B
R is shown to be about 100 times slower than the M-state of the simila
r wild type BR-film.