Energy metabolism, carbon Isotope

Figure 11.1. A flow-model scheme for treating the protein routing question. Labels refer to flow rates of carbon. The total carbon flux, into and out of the body, is 1, divided into F (for protein) and 1 - F for the remainder. The significant relevant internal fluxes are between the amino acid pool (coupled to the body protein pool), and the energy metabolism pool . The extent to which protein routing is observable in the body protein composition depends on the value ofX (See Fig. 11.2). Numbers in refer to suggested isotopic fractionations associated with a metabolic path, which are consistent with the data of the Ambrose and Norr (1993) and Tieszen and Fagre (1993) data set (see Section 4.1).

Lipids form a minor part of the carbon content of herbivore diets As a result, despite the fact that they are used primarily for energy metabolism, their abundance is not sufficient to greatly influence the isotopic composition of blood bicarbonate For this reason, the isotopic composition of lipids will not significantly affect the isotopic ratio of carbon in bone apatite ... 

Figure U. Theoretical models for carbon isotope fractionation between diet and bone in humans. Top, isotopic fractionation resulting from organism growth (major pathway emphasized) and bottom, isotopic fractionation resulting from energy metabolism (major pathways emphasized).

FIGURE 15.1 An overview of the natural variations in the carbon isotopic composition of a range of materials. Reprinted from T.B. Coplen et al. [16], with permission from Coplen. NBS, National Bureau of Standards L-SVEC, lithium carbonate IAEA, International Atomic Energy Agency NGS, natural gas standards RM, reference material CAM, Crassulacean acid metabolism USGS, U.S. Geological Survey VPDB, Vienna PeeDee Belemnite. 

The sample (biological sample or collected fraction) is oxidized to produce carbon dioxide which is then converted to graphite (Getachew et ah, 2006). The sample is then ionized, and ions are accelerated to high levels of energy in the MS. The ratio of the rare isotope to the abundant isotope is determined ( C/ C, for example). Because of the extreme sensitivity of AMS (in the attomole range), only a small amount of radio-labeled carotenoid is necessary to study absorption and metabolism. 

---