Time-resolved fluorescence studies on the internal motionof chlorophyll a of light-harvesting chlorophylla/b-protein complex in lipid membranes

By analyzing the steady state and time-resolved fluorescence anisotropy, the internal motions of chlorophyll a of light-harvesting chlorophyll a/b-protein complex (LHCII) were characterized in a dimyristoylphosphatidylcholine (DMPC) liposome. Corresponding to the thermotropic phase of the membrane, chlorophyll a showed an unique internal motion in LHCII. At the gel phase, two motional components, one fast and the other slow, were observed, which would originate in the heterogeneity of the mutual orientation and the binding site of the chlorophyll a in LHCII. Interestingly, the faster motion was suppressed and only the slower segmental rotation with the larger motional amplitude was allowed on the phasetransition to a liquid crystalline phase.