Incorporation of 19F-substituted aromatic amino acids into membrane proteins from chromatophores of Rhodospirillum rubrum G9 +

Abstract

Chromatophore membranes were isolated from cells of the carotenoidless mutant Rhodospirillum rubrum G9 + grown in the presence of several fluorinated aromatic amino acids, solubilized using SDS and the extent of incorporation analyzed using high-resolution 19F-NMR spectroscopy. 3- and 4- 19F-phenylalanine, 6- 19F-tryptophan and 3- 19F-tyrosine were biosynthetically incorporated into membrane proteins whereas 5- 19F-tryptophan and 2- 19F-phenylalanine were inhibitors of cell growth. The polypeptide chains of the major chromatophore membrane protein the light-harvesting complex, were isolated and shown by high-resolution 19F-NMR to contain 3- 19F-phenylalanine, which is known to be situated principally within the membrane hydrocarbon layer. Broad-band 19F-NMR spectra of 3- 19F-phenylalanine-labelled chromatophores showed the phenyl ring to be immobilized within the membrane.