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Control of specific growth rate in Saccharomyces cerevisiae

¹ University of Stellenbosch;
² University of Amsterdam

ABSTRACT

In this contribution we resolve the long standing dispute whether or not the Monod constant Ks, describing the overall affinity of an organism for its growth limiting substrate, can be related to the affinity of the transporter for that substrate Km. We show that the two constants can be directly related to one another via the control of the transporter on the specific growth rate; they are identical if the transport step has full control. The analysis leads to the counter-intuitive result that it is to be expected that the affinity of an organism for its substrate is higher than the affinity of the enzyme that facilitates its transport. Experimentally we show this indeed to be the case for the yeast Saccharomyces cerevisiae, for which we determined in glucose limited chemostat cultures a Km value for glucose more than two times higher than the Ks value. Moreover, we could calculate that at glucose concentrations of 0.03 and 0.29 mM the transport step controls the specific growth rate for respectively 78 % and 49 %.

³ E-mail: jls{at}sun.ac.za