Figure 2 | Scientific Reports

Figure 2

From: Low affinity uniporter carrier proteins can increase net substrate uptake rate by reducing efflux

Figure 2

High affinities can reduce the net uptake rate in facilitated diffusion models. (A) Steady-state uptake rate (J) as a function of the Michaelis-Menten contant (K M , the substrate concentration at which the half-maximal uptake rate is attained in the absence of product inhibition) of a facilitated diffusion model (solid lines) and with reversible Michaelis Menten kinetics (dashed lines), for different external substrate concentrations s e and a constant internal substrate concentration s i = 1. In a facilitated diffusion model very high affinities reduce the steady state flux, whereas for reversible Michaelis-Menten kinetics J monotonically decreases with K M . The K M was varied by varying the substrate-transporter dissociation-constants K D , which for both rate equations affects the K M but not the maximal uptake rate per transporter (k cat ). We used k2 = 1 and k4 = 8 and a total transporter concentration e t = 1. (B) Steady-state flux J glycolysis , as a function of the Michaelis-Menten constant of the glucose transporter KM,GLT, of a kinetic model of S. cerevisiae glycolysis. At an extracellular glucose concentration of 110 mM (green line) the low affinity HXT3 transporter (K M = 34 mM) is roughly optimal, with J glycolysis = 121 mM/min/L-cytosol, whereas the high affinity HXT6 transporter (K M = 1.4 mM) attains J glycolysis = 88.8 mM/min/Lcytosol. At low glucose concentrations (blue line) the high affinity transporter performs better.