Nonlinear electric response of the diffuse double layer to an abrupt charge displacement inside a biological membrane.

In order to elucidate the old, still unsolved problem of how the diffuse electric double layer responds to an abrupt, intramolecular charge displacement inside a biological membrane, we investigated the fastest components of the light-induced electric signals of bacteriorhodopsin and its mutants, in numerous ionic and buffer solutions. The obtained data for temperature and solute concentration dependence were interpreted as a consequence of changes in the capacity of the diffuse double layer surrounding the purple membrane. The possible physiological consequences of this so far not demonstrated phenomenon are discussed.

2D measurement of ion currents associated to the signal transduction of the phototactic alga Chlamydomonas reinhardtii.

Our objective was to develop a simple procedure for the detection of light-induced ion currents of photomotile cells in two dimensions. The novel technique was based on the light gradient method (LGM), and the model object was Chlamydomonas reinhardtii, a phototactic unicellular alga, ideal for such experiments. The conventional LGM cuvette was modified such that the electrode pair could be rotated around the sample and pick up the electric signals from arbitrary directions.

Optical and electric signals from dried oriented purple membrane of bacteriorhodopsins.

All the intermediates of the bacteriorhodopsin photocycle are excitable with light of suitable wavelength. This property might regulate the activity in the cells when they are exposed in the nature to high light intensity. On the other hand this property is involved in many applications.

Excitation of the M intermediates of bacteriorhodopsin.

Protein electric response signals (PERS) of the M intermediates of wild-type bacteriorhodopsin (bR) were recorded. Contrary to earlier findings reporting on a single-phase response upon excitation of the M intermediates, a kinetic analysis of the signals revealed the existence of three components, the fastest and the slowest ones of negative, while the middle one of positive sign with respect to the normal direction of proton pumping. Based on proton motion indicator experiments and molecular dipole calculations, the components were assigned to proton transfer steps and conformational changes driving the bR molecule back from the M to the ground state upon blue light excitation.

Excitation of the L intermediate of bacteriorhodopsin: electric responses to test x-ray structures.

The L intermediate of bacteriorhodopsin was excited, and its electrical response was measured. Two positive components were found in it with respect to the direction of proton pumping: an unresolved fast component, and a slower one (tau=7 micros) of small amplitude. The fast component was assigned to a charge motion corresponding to reisomerization of the retinal moiety, whereas the slow one was attributed to charge rearrangements reestablishing the ground state.