TABLE 2.
Isotopic enrichment of threitol and sorbitol observed after injections of singly 13C-labeled glucose isotopomers into the hemolymph of U. ceramboides
| 13C-Labeled carbon in glucose | Predicted position of 13C enrichment in threitol | Ratio of threitol 13C signal intensities C-1/C-4:C-2/C-3 | Predicted position of secondary 13C enrichmenta | Ratio of sorbitol13C signal intensitiesb |
|---|---|---|---|---|
| 64.2:73.1 ppm | ||||
| C-1 | No enrichment | 1.5:1 | C-6 | 1.6 |
| C-2 | No enrichment | 1:2 | C-5 | 1.7 |
| C-3 | C-1 (64.2 ppm) | 5.2 ± 1.6:1 (n = 5) | C-4 | 1.8 ± 0.6 (n = 5) |
| C-4 | C-2 (73.1 ppm) | 1:5.9 | C-3 | 1.2 |
| C-5c | C-3 (73.1 ppm) | 1:5.5 | C-2 | 2.7 |
| C-6 | C-4 (64.2 ppm) | 27.5:1 | C-1 | 2.0 |
a Secondary enrichment of sorbitol due to label scrambling via the triosephosphate isomerase reaction and subsequent gluconeogenesis.
b Predicted site of secondary enrichment relative to the average of the remaining four natural abundance sorbitol signals.
c Stock solution contained ∼90% d-[5-13C]glucose and 10% d-[6-13C]glucose.