Unilamellar vesicles are observed to form spontaneously at planar lipi
d bilayers agitated by exothermic chemical reactions, The membrane-bin
ding reaction between biotin and streptavidin, two strong transmembran
e neutralization reactions, and a weak neutralization reaction involvi
ng an ''antacid'' buffer, all lead to spontaneous vesicle formation. T
his formation is most dramatic when a viscosity differential exists be
tween the two phases bounding the membrane, in which case vesicles app
ear exclusively in the more viscous phase, A hydrodynamic analysis exp
lains the phenomenon in terms of a membrane flow driven by liberated r
eaction energy, leading to vesicle formation. These results suggest th
at energy liberated by intra- and extracellular chemical reactions nea
r or at cell and internal organelle membranes can play an important ro
le in vesicle formation, membrane agitation, or enhanced transmembrane
mass transfer.