TEMPERATURE-DEPENDENCE OF MOLECULAR MOTIONS IN THE MEMBRANE-PROTEIN BACTERIORHODOPSIN FROM QINS

The internal molecular motions of the membrane protein bacteriorhodops in (BR) have been investigated by means of quasielastic incoherent neu tron scattering (QINS). Measurements using a time-of-flight spectromet er were performed in order to study the quasielastic scattering compon ent in the temperature range 100-297 K. Within an energy range of +/- 1.5 meV, it is possible to fit the data by a single Lorentzian with a line width of 100 mu eV (HWHM). The line width of the quasi-elastic co mponent is roughly T- and Q-independent. The intensity of the quasiela stic scattering is negligible below 200 K and shows a pronounced incre ase above this temperature, which is caused by an appearance of therma l fluctuations leading to transitions between different conformational substates of BR.