Determining biological tissue turnover using stable isotopes: the reaction progress variable
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The reaction progress variable is applied to stable isotope turnover of biological tissues. This approach has the advantage of readily determining whether more than one isotope turnover pool is present; in addition, the normalization process inherent to the model means that multiple experiments can be considered together although the initial and final isotope compositions are different. Consideration of multiple isotope turnover pools allows calculation of diet histories of animals using a time sequence of isotope measurements along with isotope turnover pools. The delayed release of blood cells from bone marrow during a diet turnover experiment can be quantified using this approach. Turnover pools can also be corrected for increasing mass during an experiment, such as when the animals are actively growing. Previous growth models have been for exponential growth; the approach here can be used for several different growth models.
KeywordsHalf-life First-order rate constant Carbon isotopes Turnover Stable isotopes
This work was partially funded by IsoForensics; T. E. C. and J. R. E. have financial ties to IsoForensics. We are grateful for the support provided by the SIRFER laboratory at the University of Utah. The work on woodrats was supported by NSF grant IN0236402 to M. D. D. We thank Brian Popp, Don Phillips, and an anonymous reviewer for useful comments.
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