A. Boyer et al., COLOR DISCRIMINATION BY FORWARD AND REVERSE PHOTOCURRENTS IN BACTERIORHODOPSIN-BASED PHOTOSENSOR, Biosensors & bioelectronics, 10(5), 1995, pp. 415-422
The photocurrent response of bacteriorhodopsin is measured for purple
membrane solid films at an electrode/electrolyte interface upon revers
ible transformation of the native bR(570) pigment into a structurally
and spectrally modified bR(480) form, in the presence of the halogenat
ed general anaesthetic Enflurane. The reversible pigment transformatio
n is accompanied by a reversible inversion of the photocurrent signal.
Action spectra of these forward and reverse photocurrent patterns hav
e their maxima at 570 and 480 nm, respectively, and indicate that the
two bacteriorhodopsin spectral forms have their own characteristic pho
toresponse. The time-resolved photoresponse curves of bR(570) and bR(4
80) both show the characteristic sequence of capacitive currents which
accompany the photochemical activity of bacteriorhodopsin. However, l
ike their respective differential photoresponse, the algebraic sums of
their respective photocurrent components have opposite signs. The for
ward and reverse photoresponse patterns thus have their origin in the
charge displacement currents particular to each spectral species. This
indicates that purple membranes readily self-orient upon deposition o
nto an electrode. This orientation is maintained upon pigment transfor
mation by the anaesthetic, even if it leads to an inverted photorespon
se, suggesting a capacitive, rather than rectifying, character of the
pigment/electrode junction.