  Shape transformations of flat bilayer membranes and vesicles induced by
hydrolysis and condensation reactions of amphiphilic molecules are studied
using coarse-grained molecular dynamics simulations. The hydrolysis and
condensation reactions result in the formation and dissociation of amphiphilic
molecules, respectively. Asymmetric reactions between the inner and outer
leaflets of a vesicle can transport amphiphilic molecules between the leaflets.
It is found that the resulting area difference between the two leaflets induces
bilayer sheet protrusion~(BP) and budding at low reduced volumes of the
vesicles, whereas BP only occurs at high reduced volumes. The probabilities of
these two types of transformations depend on the shear viscosity of the
surrounding fluids compared to the membrane as well as the reaction rates. A
higher surrounding fluid viscosity leads to more BP formation. The
inhomogeneous spatial distribution of the hydrophobic reaction products forms
the nuclei of BP formation, and faster diffusion of the products enhances BP
formation. Our results suggest that adjustment of the viscosity is important to
control membrane shape transformations in experiments.
