Fig. 5.

Influence of two-bond ¹³C–¹³C J couplings on measured R ₂ relaxation decays. a ¹³C incorporation pattern in a Phe side chain resulting from labeling with 1-¹³C₁-glucose. Black circles represent ¹³C-labeled positions while open circles represent ¹²C. The symbols to the right of the aromatic rings show the net percentages of labeled or unlabeled sites (labeled/unlabeled), and the percentages of ¹³C sites with or without a two-bond neighbor (labeled–labeled/labeled–unlabeled). Labeling using 100 % 1-¹³C₁-glucose yields 50 % ¹³C incorporation in the Cδ positions, and 50 % of these ¹³Cδ have a ¹³C-labeled two-bond neighbour. Labeling using 50 % 1-¹³C₁-glucose + 50 % ¹²C₆-glucose reduces the relative number of labeled carbons, as well as that of labeled two-bond neighbours, to 25 %. b Representative R ₂ relaxation decays for different aromatic side chains in samples labeled using 100 % 1-¹³C₁-glucose (filled circles) or 50 % 1-¹³C₁-glucose + 50 % ¹²C₆-glucose (open circles)