TABLE 2.

Summary of the kinetic experiments for [¹³C_x] amino acids by LR-LC/MS-MS

[13Cx] amino acid	Rise to maximum (h)	Decay to baseline (h)	Possible carbon positions involved
[13C1]Ala, not 1-C	1–6	>24	2 or 3
[13C2]Ala	<1	>24	2, 3 mainly
[13C1]Glu, 1-C	1–6	12	1
[13C1]Glu, not 1-C	1	12	2, 3, 4, 5
[13C2]Glu, 1-C	1–6	12	1, 2, 3, 4, 5
[13C2]Glu, not 1-C	1	12	2, 3, 4, 5
[13C3-4]Glu, 1-C	1	12	1, 2, 3, 4, 5
[13C1]Gln, 1-C	6	>12	1
[13C1]Gln, not 1-C	6	>12	2, 3, 4, 5
[13C2]Gln, 1-C	1–6	>12	1, 2, 3, 4, 5
[13C2]Gln, not 1-C	1–6	>12	2, 3, 4, 5
[13C3]Gln, 1-C	6	>12	1, 2, 3, 4, 5
[13C1]Pro, 1-C	1–6	>12	1
[13C1]Pro, not 1-C	1–6	>12	2, 3, 4, 5
[13C2]Pro, 1-C	1	>12	1, 2, 3, 4, 5
[13C2]Pro, not 1-C	1	>12	2, 3, 4, 5
[13C3–4]Pro, 1-C	1–6	>12	1, 2, 3, 4, 5
[13C3–4]Pro, not 1-C	1–6	>12	2, 3, 4, 5

Rise and decay times are estimated from the kinetics data shown in Figs. 2 and 3. The term “1-C” refers to the first carbon position in the amino acid backbone.