N-like intermediate in the photocycle of the acid purple form of bacteriorhodopsin.

The photocycle of the acid-purple form of bacteriorhodopsin (BR) was studied by multiwavelength absorption kinetic measurements. The data were evaluated using a new method based on the differences in the kinetics of the absorption changes at different wavelengths [Tokaji, Zs. (1995) FEBS Lett. 357, 156-160]. The evaluation indicates that, in contrast to the previous suggestion, the photocycle of the acid purple BR contains an intermediate that, in its spectral and kinetic properties, resembles the N intermediate of the alkaline BR photocycle.