Table 1.

Labeling of free metabolites, derived with BSTFA, showing changes of labeling pattern under hypoxic condition (n = 2)

Synthesis from central pathways	Metabolites	Aerobic		Hypoxia for 3.5 h
		(M − 15)+ or *f(218)+	(M − 117)+	(M − 15)+ or f(218)+	(M − 117)+
Glycolysis pathway	Alaa
	M0	Overlapping peak	0.08 ± 0.02	Overlapping Peak	0.10 ± 0.01
	M1		0.89 ± 0.03		0.88 ± 0.01
	M2		0.02 ± 0.01		0.02 ± 0.01
	Pyruvateb
	M0	0.02 ± 0.02	Overlapping peak	0.12 ± 0.02	Overlapping Peak
	M1	0.94 ± 0.03		0.82 ± 0.02
	M2	0.04 ± 0.02		0.05 ± 0.01
	M3	0.02 ± 0.01		0.01 ± 0.01
	Gly
	M0	0.10 ± 0.02	0.27 ± 0.01	0.26 ± 0.01	0.37 ± 0.01
	M1	0.86 ± 0.02	0.73 ± 0.01	0.71 ± 0.01	0.63 ± 0.01
	M2	0.03 ± 0.01	0	0.03 ± 0	0
	Serc
	M0	0.09 ± 0.02*	0.09 ± 0.04	0.15 ± 0.01*	0.17 ± 0.01
	M1	0.88 ± 0.01*	0.83 ± 0.07	0.81 ± 0.04*	0.69 ± 0.04
	M2	0.03 ± 0.02*	0.08 ± 0.03	0.04 ± 0.03*	0.13 ± 0.04
Pentose phosphate pathway	Phed
	M0	0.10 ± .0.03*	0	0.12 ± 0.03*	0
	M1	0.85 ± 0.03*	0	0.86 ± 0.04*	0
	M2	0.04 ± 0.01*	0.06 ± 0.02	0.01 ± 0.01*	0.08 ± 0.02
	M3	0	0.66 ± 0.04	0	0.64 ± 0.04
	M4	0	0.22 ± 0.03	0	0.21 ± 0.03
TCA cycle	Aspe
	M0	Insufficient ions	0.11 ± 0.01	Insufficient ions	0.21 ± 0.02
	M1		0.63 ± 0.02		0.59 ± 0.01
	M2		0.25 ± 0.03		0.19 ± 0.02
	M3		0.01 ± 0.01		0.01 ± 0.01
	Glu
	M0	0.01 ± 0	0.03 ± 0.01	0.03 ± 0.01	0.07 ± 0.02
	M1	0.15 ± 0.03	0.24 ± 0.04	0.23 ± 0.03	0.39 ± 0.04
	M2	0.63 ± 0.04	0.69 ± 0.05	0.52 ± 0.04	0.49 ± 0.04
	M3	0.21 ± 0.03	0.05 ± 0.02	0.18 ± 0.03	0.04 ± 0.02
	Citratef
	M0	Insufficient ions	0.38 ± 0.05	Insufficient ions	0.58 ± 0.07
	M1		0.21 ± 0.04		0.23 ± 0.06
	M2		0.29 ± 0.04		0.14 ± 0.02
	M3		0.11 ± 0.02		0.04 ± 0.01
	M4		0.01 ± 0		0.01 ± 0
	Succinateg
	M0	0.05 ± 0.01	Not fragmented	0.12 ± 0.02	Not fragmented
	M1	0.22 ± 0.03		0.40 ± 0.04
	M2	0.66 ± 0.04		0.41 ± 0.03
	M3	0.05 ± 0.01		0.06 ± 0.03

Note: The final isotopomer data were reported as M0 unlabeled fraction, M1 singly labeled fraction, M2 fraction with two labeled carbons, M3 fraction with labeled three carbons, etc. *f(218)⁺ peak is used instead of (M − 15)⁺. (1) Alanine’s (M − 15)⁺ peak overlaps the f(218)⁺ peak. (2) Pyruvate’s (M − 117)⁺ peak overlaps other anomalous ion peaks. (3) Serine’s f(218)⁺ fragment is better for quantitative purposes than (M − 15)⁺ due to high signal to noise ratio in the latter. (4) Phenylalanine’s f(218)⁺ fragment is better for qualitative purposes used for these amino acids than (M − 15)⁺ due to high signal to noise ratio in the latter. (5) Aspartic acid’s (M − 15)⁺ and f(218)⁺ peak have high background noise. Not recommended to be used. (6) Citrate (M − 117)⁺ fragment is better for quantitative purposes than (M − 15)⁺ due to high signal to noise ratio in the latter. (7) Succinate’s (M − 117)⁺ ion is not present, i.e., MS cannot fragment succinate