Deuterium nuclear magnetic resonance study of amino acid dynamics in the membrane protein, bacteriorhodopsin

Deuterium (2H) Fourier transform nuclear magnetic resonance (NMR) spectra for many polycrystalline, deuterium-labelled amino acids in the solid state have been obtained. Where possible, these have been biosynthetically incorporated into the membrane protein, bacteriorhodopsin in the photosynthetic purple membrane of Halobacterium halobium. Deuterio-methyl group spin lattice relaxation times have been obtained as a function of temperature. The results yield the Arrhenius activation energies for methyl rotation, and through the use of a suitable mathematical model, rotation correlation time. The results are analyzed using a mathematical model for two-fold flipping about the C2 axis. Overall, the results demonstrate a similarity between the dynamics in amino acid crystals and in membrane proteins