REVERSIBLE INHIBITION OF PROTON RELEASE ACTIVITY AND THE ANESTHETIC-INDUCED ACID-BASE-EQUILIBRIUM BETWEEN THE 480 AND 570 NM FORMS OF BACTERIORHODOPSIN

In purple membrane added with general anesthetics, there exists an aci d-base equilibrium between two spectral forms of the pigment: bR(570) and bR(480) (apparent pK(a) = 7.3). As the purple 570 nm bacteriorhodo psin is reversibly transformed into its red 480 nm form, the proton pu mping capability of the pigment reversibly decreases, as indicated by transient proton release measurements and proton translocation action spectra of mixture of both spectral forms, It happens in spite of a co mplete photochemical activity in bR(480) that is mostly characterized by fast deprotonation and slow reprotonation steps and which, under co ntinuous illumination, bleaches with a yield comparable to that of bR( 570). This modified photochemical activity has a correlated specific p hotoelectrical counterpart: a faster proton extrusion current and a sl ower reprotonation current. The relative areas of all photocurrent pha ses are reduced in bR(480), most likely because its photochemistry is accompanied by charge movements for shorter distances than in the nati ve pigment, reflecting a reversible inhibition of the pumping activity .