Energy metabolism, carbon Isotope fractionation

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 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).

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. 

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