THE ROLE OF THE POSITIVELY CHARGED AMINO ACIDS IN BACTERIORHODOPSIN

This study has used chemical modification techniques to investigate the role of the only two types of positively charged amino acids, lysines and arginines, in the membrane-bound protein, bacteriorhodopsin (bR) • The results of these chemical modifications have significance both for the structure of bR and for the molecular mechanism of light-activated photocycling and proton pumping. The implications for the secondary structure of bR are: LYS 40 is totally exposed to the aqueous phase, while the other five reactive lysines are partially buried in the hydrophobic domain; LYS 30, LYS 129 and LYS 159 are buried by only one or two residues within the hydrophobic domain; all but two arginines are totally exposed to the aqueous phase; and at least three ionic bridges form between arginines and carboxyl groups. These results were used to construct a new model of the secondary structure of bR. The impli