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-specifi c mutagenesis is known to change the position and orientation of the p rotonated Schiff base relative to Asp85 within the retinal cavity of b acteriorhodopsin (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 photoisomeri zation of retinal in bR is examined by using a pump-probe technique. A decrease in the rate of photoisomerization of retinal in V49A and A53 V is observed. This is discussed in terms of the previously proposed m echanism of the protein catalysis to the retinal photoisomerization pr ocess in bR.