Fig. 5

Complex formation of sterol in either PM leaflet compared to the ER sets the steady state sterol ratio between both compartments. Steady state sterol distribution between PM and ER (Eq. 46) as a function of equilibrium constant for sterol complex formation in the outer leaflet (a varying q₄) or in the inner leaflet of the PM (b varying q₅) for differing values of the equilibrium constant for sterol complex formation in the ER. We set q₂ = q₃ = 1, meaning that forward and backward rate constants for sterol flip flop and for exchange between PM and ER, respectively, are identical. Parameters were k₃ = 0.1 s^− 1, k₂ = 1 s^− 1and K₇ = 0.01 s^− 1, respectively. The equilibrium constant for the complex formation in the corresponding other leaflet was kept constant to q₅ = 0.5 in (a) and q₄ = 0.5 in (b). See text for further explanations