Circadian systems and metabolism

Circadian systems direct many metabolic parameters and, at the same time, t hey appear to be exquisitely shielded from metabolic variations. Although t he recent decade of circadian research has brought insights into how circad ian periodicity may be generated at the molecular level, little is known ab out the relationship between this molecular feedback loop and metabolism bo th at the cellular and at the organismic level. In this theoretical paper, we conjecture about the interdependence between circadian rhythmicity and m etabolism. A mathematical model based on the chemical reactions of photosyn thesis demonstrates that metabolism as such may generate rhythmicity in the circadian range. Two additional models look at the possible function of fe edback loops outside of the circadian oscillator. These feedback loops cont ribute to the robustness and sustainability of circadian oscillations and t o compensation for long- and short-term metabolic variations, The specific circadian property of temperature compensation is put into the context of m etabolism. As such, it represents a general compensatory mechanism that shi elds the clock from metabolic variations.