ANALYZING THE RED-SHIFT CHARACTERISTICS OF AZULENIC, NAPHTHYL, OTHER RING-FUSED AND RETINYL PIGMENT ANALOGS OF BACTERIORHODOPSIN

Prompted by the near infrared-absorbing properties of some of the azul enic bacteriorhodopsin (bR) analogs, we have analyzed their absorption characteristics along with 11 new related ring-fused analogs and the corresponding Schiff bases (SB) and protonated Schiff bases (PSB). The following three factors are believed to contribute to the total red s hift of each of the pigment analogs (Sigma(RS)): perturbation of the b asic chromophore (SB shift, Delta SB), protonation of the SB (PSB shif t, PSBS) and protein perturbation (the opsin shift, OS). For each fact or, effects of structural modifications were examined. For the red-shi fted pigments, percent OS has been suggested as an alternate way of me asuring protein perturbation. Computer-simulated chromophores provided evidence against any explanation involving altered shapes of the bind ing pocket as a major cause for absorption differences. Implications o f the current bR results on preparation of further red-shifted bR and possible application to visual pigment analogs are discussed.