Bacteriorhodopsins containing modified chromophores: A study on the wild type and D96N mutant of Halobacterium salinarum

Modification of the chromophore in bacteriorhodopsin (BR) from ET1001 and D96N strains of Halobacterium salinarum (halobium) was carried out. Purple membranes were decolored by means of light-dependent hydroxylaminolysis. The all-trans -isomers of retinal and its 3,4-didehydro-, 4-keto-, and phenyl analogs were reconstituted into apomembranes. Absorption maxima of the homonymic pigments in both strains were similar. The kinetics of the M-intermediates in the mode of a single turnover of the photocycle induced by a short light flash (532 nm, 15 ns) was compared. For the investigated bacteriorhodopsin analogs the efficiency of the M-intermediate formation did not exhibit any reliable dependence on the point mutation. Both for ET1001 and for D96N strains the M-relaxation of the 4-ketoBR was distinctly biphasic, with the slow phase comprising about 10–15% of the signal amplitude. Replacement of the ionone ring by phenyl caused a weak deceleration of the M relaxation (～1.5-fold decrease in t _1/2). Independence of the photocycle deceleration of the point mutation and chromophore modification was shown for all BR analogs studied.