The molecular motion of bacteriorhodopsin mutant D96N in the purple membrane

We measured the flash-induced absorption anisotropies of mutant bacteriorhodopsin (bR), D96N, in the purple membrane suspension. The measured anisotropy decay at 410 nm differed from that at 570 nm. These wavelength-dependent anisotropies show that the motion of absorption dipole of non-excited bR is faster than that of M-intermediate. The motion of non-excited bR is considered as the rotational motion of whole protein in the purple membrane. This fact suggests that the photo-excitation induces the conformational change of the protein and/or the inter-protein interaction within the membrane, which prevents the motion of M-intermediate.