As shown in Fig. , spherical particles of radius R = 60 nm approximate enzymatic BMCs dispersed in a spherical vesicle of radius 50R. Substrate molecules (e.g., 1,2-propanediol) form a concentration field c(r s ), introduced from the +z side, yielding a boundary concentration c 0 + ξ z at the vesicle surface. The substrate-BMC interaction potential U is assumed attractive.