Volume 7, Number 4, p.p. 147–151
pH-dependence of the photoelectric response of the M intermediate of bacteriorhodopsin
R. Tóth-Boconádi, 1 S.G. Taneva, 2 L. Fábián, 1 A. Dér1,* and L. Keszthelyi1
1Institute of Biophysics, Biological Research Centre, Hungarian Academy of Sciences, P.O.Box 521, 6701 Szeged, Hungary
2Unidad de Biofísica y Departamento de Bioquímica y Biología Molecular, Universidad del País Vasco, 48080 Bilbao, Spain
The pH-dependence of the protein electric response signals (PERS) of the M intermediate states of wild type bacteriorhodopsin (bR) and its D96N mutant have been recorded. Kinetic analysis of the signals revealed the existence of three components, the fastest and the slowest being negative, and the middle intermediate one being positive with respect to the normal direction of proton pumping. It was found that the amplitudes and time constants of the first two components did not change with pH, while those of the third component increased with increasing pH. Based on a contemporary photocycle model and X-ray data, 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.
Keywords: charge motion; conformational changes, photocycle, proton transport