Abstract
The proton pump activity of bacteriorhodopsin in aqueous solution upon excitation with modulated continuous light was monitored electrochemically and analyzed by superimposing a series of transient proton translocation events H i + (t). An evolution function f (t) = h e -l t + k h + k, including a decay and a stationary offset, was introduced to weight the contribution of the individual transient events evolving with time in the envelope of the steady-state event. The evolution of the total proton concentration can be treated as an ensemble of weighted sequential transient events, H t o t a l + (t) = E i n = 0 H i + (t). f (t), and the temporal profile of the photocurrent is derived by differentiating the proton concentration with respect to time, I (t) ∝d H t o t a l + (t) d t. The temporal profiles of the bacteriorhodopsin photocurrent in pH range of 6.3-8.1 were analyzed using a well-defined kinetics model and restricted mathematical formulization, and fitted temporal behaviors agreed with the observations. This successful proof-of-concept study on analyzing a steady-state phenomenon using an ensemble of sequential transient events can be generalized to quantify other phenomena upon continuous stimulation, such as estimation of the light-driven ion pump activities of the photosynthetic proteins upon illumination.