LOW-TEMPERATURE RETINAL PHOTOISOMERIZATION DYNAMICS IN BACTERIORHODOPSIN

Retinal photoisomerization dynamics are studied at both room temperatu re and 20 K in wild-type bacteriorhodopsin using femtosecond pulses. W e were able to resolve the decay at 20 K into two components with the dominant component having a similar lifetime to that observed at room temperature. This strongly suggests that the retinal lifetime at physi ological temperature is barrierless. The minor, low-temperature long-l ived component is discussed in terms of previous results obtained for fluorescence and transient absorption with lower time resolution, and the origin of this component is discussed in terms of low-temperature glass heterogeneity.