Long time stability of purple membranes from Halobacterium halobium.

The fast component of the electrical signal and the light absorption signals at different resolution times (at lambda = 408 nm) in an untreated purple membrane suspension were measured in order to study the stability of purple membrane fragments. It has been established that there is no change in the rate constants of L----M and M----O transitions of the photocycle in either the electrical or the light absorption signals of purple membrane suspension kept at 4 degrees C for up to 40 days. Moreover, also the amplitudes of the I (negative) and II (positive) components of the electrical signal remained unchanged during this period.