Motions and structures of chromatophore of a photosynthetic bacterium ( Chromatium vinosum) as revealed from carbon-13 and phosphorus-31 NMR

Abstract

Carbon-13 enriched-chromatophore was prepared from a 13C-enriched culture of a photosynthetic bacterium ( Chromatium vinosum) with a purpose to investigate the dynamic structures of photosynthetic membranes and proteins by 13C-NMR spectra which were observed in a relatively resolved state at 75.46 MHz (under a 7.05 T static magnetic field). This was in clear contrast with phosphorus-31 NMR spectra of chromatophore with broad band signals. The 13C-NMR was assigned to signals essentially from lipids (mostly phospholipids with a small amount of galactolipids). Linewidths of 13C-NMR signals of an intact chromatophore were narrowed on addition of detergents such as Triton X-100, sodium dodecyl sulfate (SDS), and lauryl- N, N-dimethylamine N-oxide (LDAO). Particularly the line-narrowing effect by Triton X-100 was remarkable among them. High resolution 31P-NMR spectra of phospholipid in a chromatophore were observed only in the presence of detergents. Spin-lattice relaxation times ( T 1's) of the lipid 13C-NMR signals in chromatophore indicate a low mobility of the polar head groups of the lipids, which was interpreted to indicate the presence of the interactions between the polar head groups of the lipids with proteins.