Solid state NMR experiments will be employed to investigate three membrane proteins -- Bacteriohodopsin (bR), Rhodopsin (RHO), and Halorhodopsin (hR). The bR investigations will focus on (1) improving our understanding of the Opsin Shift in bR through optical and NMR studies of 6-s-trans model compounds; (2) elucidation of the proton translocation mechanism through 13C-15N rotational echo double resonance (REDOR) and 13C-13C rotational resonance (R2) determinations of the Lys-216 sidechain conformation; (3) high resolution 1H NMR studies designed to determine the existence and structure of the hydrogen bonded chain; (4) low temperature trapping and detection of the protonation/deprotonation of amino acid sidechains such as Tyr and Asp in bR photointermediates; (5) 19F-19F and 13C-13C rotational resonance experiments designed to determine the location of Trp's and Tyr in the retinal binding pocket. The hR experiments will be aimed at studying the opsin shift mechanism in this protein, the state of the two His residues, and the binding of anions. Finally, the RHO experiments will focus on chromophore structure in bathorhodopsin and will rely on comparison of chemical shifts between RHO, isorhodopsin, and batho. Large perturbations in the shifts will be investigated further with R2 structural studies. In particular, R2 lineshapes will be employed to search for twist about single (and perhaps double) bonds in the photo excited chromophore.