Cooperative phenomena in the photocycle of D96N mutant bacteriorhodopsin.

The M intermediate decay in the photocycle of D96N mutant bacteriorhodopsin does not depend on the light intensity of the exciting flash. Cooperative phenomena in the photocycle are revealed after addition of azide causing acceleration of the M decay and making it kinetically well separated from the N decay. Increase in the light intensity induces slight deceleration of the M decay and significant acceleration of the N decay. The data obtained directly confirm our recent model [Komrakov and Kaulen (1995) Biophys. Chem. 56, 113-119], according to which appearance of the Mslow intermediate in the photocycle of the wild type bR at high light intensity is due to destabilization of the N intermediate leading to the acceleration of the N-->M and N-->bR reactions.