Flux of labeled compounds in biochemical oscillations

If a labeled compound (e.g., a radioisotopically or chemically labeled metabolite) is introduced into any biochemical reaction system, the label will be removed by catabolic reactions and replaced by unlabeled compound through anagolic reactions. It is shown that the removal of labeled compounds is particularly efficient if the rates of the catabolic steps are able to oscillate. This is demonstrated by comparing reaction schemes that maintain the same mean fluxes and concentrations of metabolites and the same overall chemical affinity but which differe in that the rate of catabolism is either constant or oscillates as a function of time. Simple analyses are presented for both small and large oscillations of undefined wave form and for sinusoidal oscillations. The enhanced removal of labeled compounds from oscillating reaction systems is also documented by numerical computation on a nonlinear model system. It is suggested that this ability to remove labeled compounds may have provided a selective advantage for the evolution of some biological oscillations.