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

By analyzing the steady state and time-resolved fluorescence anisotropy, th e internal motions of chlorophyll a of light-harvesting chlorophyll a/b-pro tein 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 bind ing site of the chlorophyll a in LHCII. Interestingly, the faster motion wa s suppressed and only the slower segmental rotation with the larger motiona l amplitude was allowed on the phase transition to a liquid crystalline pha se.