Water activity at interfaces and its role in regulation of interfacial enzymes: a hypothesis

A simple relationship between surface pressure and interfacial water activity has been derived. It is hypothesized that the mechanism of activation of several membrane-bound enzymes by the surface pressure of the membrane might in part be related to changes in interfacial water activity. That is, the lipid-water interface of biomembranes may provide a thermodynamic environment in which the (re)activity of water can be controlled very precisely by inducing localized changes in surface pressure. This precise control of local water activity at interfaces might be one of the mechanisms by which the activities of membrane-bound enzymes are regulated in biological systems. The surface pressure dependency of activities of some of the membrane-bound enzymes is examined as an example in the context of interfacial water activity. (C) 1998 Elsevier Science B.V. All rights reserved.