Figure 4

Effects of intrinsic noise on the inhibition of enzyme activity in small compartments. (Model III) Plots of normalized enzyme activity versus normalized inhibitor concentration (measured in units of the total enzyme concentration [E _T ]) for 10 enzymes with K _M = 100 μM in compartments of diameter 50 nm and 100 nm (inset). The colors correspond to: (red) MM equation; (green) stochastic model, M = 20; (blue) stochastic model, M = 50. The latter two curves are those predicted by theory [Eqs. (7) and(12)]. Parameters same as mentioned in caption of Table 3 (except for [I], which is a variable in the present case). Substrate concentrations chosen so that at [I] = 0, v/v _max = 0.909 in all cases. Black dashed lines contrast the inhibitor concentration required to decrease enzyme activity from 0.909 to 0.1 as predicted by the MM equation and the stochastic models. Note that v/v _max = α _M and α for solid red and blue/green lines respectively.