Quantitative Carbon-13 Nuclear Magnetic Resonance Spectroscopic Study of Mobile Residues in Bacteriorhodopsin

We have used quantitative carbon-13 nuclear magnetic resonance (NMR) spectroscopy to study the dynamic structure of the backbone of bacteriorhodopsin in the purple membrane of Halobacterium halobium R₁and JW-3. NMR experiments were performed using an internal sucrose quantitation standard on purple membranes in which one of the following¹³C'-labeled amino acids had been biosynthetically incorporated: glycine, isoleucine, leucine, lysine, phenylalanine, and valine. the results suggest that the C-terminus of the polypeptide chain backbone, and possibly one of the connecting loops, undergoes rapid, large angle fluctuations. Our results are compared with previous NMR and fluorescence spectroscopic data obtained on bacteriorhodopsin.