Theorical and experimental model for Carbon-13 turnover in mammalian and avian tissues

Abstract

Food source differences of about 14 from plants with carbon-3 (C3) and carbon-4 (C4) photosynthetic cycles and their derived products make carbon metabolism studies possible in birds and small mammals. The authors suggest a theorical and experimental model for determining the relative enrichment results, delta per thousand (delta) of the 13C/12C ratio as a function of time for different tissues. The following equation was used: y(t) = (y0 -- q/k) e-kt + q/k where, y(t) is the isotopic concentration at time t, y0 is the initial isotopic concentration in the tissue, k is the turnover constant expressed in 1/time, and q is the input of metabolites which contain carbon expressed in delta/time. The equation below was obtained from the analysis of hen livers, the carbon-4 photosynthetic cycle ration of which was switched to a carbon-3 diet: delta13C = -24.74 + 12.37 e-0.237(nT) with 2.9 day half-life. The carbon switching steady-state was reached at --24.48 so that nearly 98.4% of the C4 isotopic content in the liver was replaced by C3 after 5.6 half-lives. The proposed model is suitable to determine the partial or entire turnover of carbon concentration in some selected tissues.