- Solution NMR spectroscopy of [alpha -15N]lysine-labeled rhodopsin: The single peak observed in both conventional and TROSY-type HSQC spectra is ascribed to Lys-339 in the carboxyl-terminal peptide sequence. Klein-Seetharaman, J., Reeves, P.J., Loewen, M.C., Getmanova, E.V., Chung, J., Schwalbe, H., Wright, P.E., Khorana, H.G. Proc. Natl. Acad. Sci. U.S.A. (2002)