Fig. 4

Preferred complex formation of sterol in the inner leaflet counteracts increasing sterol release rates in attaining sterol asymmetry in the PM. Steady state transbilayer sterol distribution (ratio Q∙M, Eq. 32) as 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). The vertical dotted grey line indicates the equilibrium constant for the complex formation in the corresponding other leaflet (i.e., q₅ = 1 in a; q₄ = 1 in b). While k₃ was varied as shown in panel (a), flip-flop rate constants were set to k₂ = k_− 2 = 1 s^− 1, respectively. A ratio Q∙M = 1 corresponds to a symmetric sterol distribution between both leaflets, while Q∙M > 1; Q∙M < 1 means sterol enrichment in the inner and outer leaflet, respectively