A sustained decrease in the intracellular ATP concentration has been observed when extra glucose was added to yeast cells growing aerobically under glucose limitation. Because glucose degradation is the main source of ATP-derived free energy, this is a counter-intuitive phenomenon, which cannot be attributed to transient ATP consumption in the initial steps of glycolysis. We present a core model for aerobic growth in which glucose supplies carbon, as well as free energy, for biosynthesis. With Metabolic Control Analysis and numerical simulations, we demonstrate that the decrease in the ATP concentration can be reproduced if the biosynthetic route is more strongly activated by carbon substrates than is the catabolic (ATP-producing) route.

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