From the electric signals measured after photoexcitation, the electrogenici
ty of the photocycle intermediates of bacteriorhodopsin were determined in
a pH range of 4.5-9. Current measurements and absorption kinetic signals at
five wavelengths were recorded in the time interval from 300 ns to 0.5 s.
To fit the data, the model containing sequential intermediates connected by
reversible first-order reactions was used. The electrogenicities were calc
ulated from the integral of the current signal, by using the time-dependent
concentrations of the intermediates, obtained from the fits. Almost all of
the calculated electrogenicities were pH independent, suggesting that the
charge motions occur inside the protein. Only the N intermediate exhibited
pH-dependent electrogenicity, implying that the protonation of Asp(96), fro
m the intracellular part of the protein, is not from a well-determined prot
on donor. The calculated electrogenicities gave good approximations of all
of the details of the measured electric signals.