Theoretical analysis of active transport through a reversed bienzyme porous membrane. II. Transport of an uncharged, small, hydrophilic molecule

Theoretical analysis of the active transport of an uncharged solute through a reversed bienzyme porous membrane separating two compartments is presented. The main parameters taken into account in the corresponding model were analyzed in terms of their impact, both on the final substrate surconcentration (SR) ratio and on the final product pollution level expected in the receiving compartment of a diffusion cell. Compared to our earlier analysis dealing with the transport of a negatively charged solute, this analysis corroborates that an active transport may occur only if three key factors act together and simultaneously: (i) bound reversed enzyme activities must exist at the pore entrance/exit; (ii) the first enzyme of the reactional sequence involved acts in an unstirred layer facing the feed compartment; (iii) to perform active transport of an uncharged substrate, the negatively charged intermediary product must be attracted by the positive charges within the membrane's pores. Once again, it was found that the unstirred layer facing the feed chamber governs the substrate SR expected in the opposite receiving chamber, while the unstirred layer facing the receiving chamber plays a role only on this transport rate. A global synthesis, underlining the different possibilities of such “intelligent” membranes, is also presented.