Table 1.

¹³C enrichment levels at various carbon positions within ribonucleotides harvested from DL323 E. coli grown on ¹³C-1,3-glycerol with and without ¹³C-formate as carbon sources

Carbon position labeled	13C-Carbon source: 1,3-Glycerol only	13C-Carbon source: 1,3-Glycerol and Formate
Purinea
Ade C2	0.88 ± 0.04	0.82 ± 0.13
C8	0.92 ± 0.07	0.81 ± 0.13b
Pyrimidinea
C5	0.88 ± 0.04	0.92 ± 0.03
C6	<0.05	0.22 ± 0.02
Ribose
C1′a	0.58 ± 0.08	0.47 ± 0.11
C2′b	0.50 ± 0.04	0.57 ± 0.09
C3′b	0.93 ± 0.01	0.77 ± 0.07
C4′b	<0.02	<0.02
C5′c	0.94 ± 0.03	0.85 ± 0.06

^aThe percentage label is calculated as an average of three methods: (i) the ratio of the sum of the intensities of satellite peaks to the sum of the intensities of the satellite and center peaks using the 2-bond ¹⁵N HSQC without ¹³C decoupling during acquisition (Dayie and Thakur 2010); (ii) the ratio of the sum of the intensities of satellite peaks to the sum of the intensities of the satellite and center peaks using the 1D ¹H experiment without ¹³C decoupling during acquisition and (iii) using the fractional enrichment (Frac_E_i) method of Lundström et al. (2007) as described in the text. We find that direct 1D and 2D methods (i and ii) give consistently slightly higher values than the fractional enrichment method (iii)

^bThe percentage label (Plabel) is calculated as in (a) but this time with only method (iii)

^cThe percentage label (Plabel) is calculated as in (a) but this time with only methods (ii) and (iii)