Effect of Changing the Position and Orientation of Asp85 Relative to the Protonated Schiff Base within the Retinal Cavity on the Rate of Photoisomerization in Bacteriorhodopsin

Replacement of either Val49 with Ala or Ala53 with Val by site-specific mutagenesis is known to change the position and orientation of the protonated Schiff base relative to Asp85 within the retinal cavity of bacteriorhodopsin (bR) (Brown, L. S.; Gat, Y.; Sheves, M.; Yamazaki, Y.; Maeda, A.; Needleman, R.; Lanyi, J. K. Biochemistry 1994, 33, 12001). The effect of mutation on the rate of the subpicosecond photoisomerization of retinal in bR is examined by using a pump−probe technique. A decrease in the rate of photoisomerization of retinal in V49A and A53V is observed. This is discussed in terms of the previously proposed mechanism of the protein catalysis to the retinal photoisomerization process in bR.