Regulation of surface-membrane enzymes by lipid ordering. A model based on allosteric transition theory

This paper shows for the first time that effects of lipid ordering on the activity of surface-membrane enzymes can be interpreted in terms of the two-state allosteric transition theory. In this mathematical modelling, the conversion of an active molecule into a catalytically inactivated one of a given enzyme can be directly triggered by a change in the order parameter of lipids. Depending on the lipid order, the tendency for this conversion is either independent of the state of other enzyme molecules or co-operatively aided through intermolecular interactions that in turn depend on lipid ordering. The theory so developed is then applied to (Na+ + K+)-dependent adenosine triphosphatase (EC 3.6.1.3). On comparison of the relevant theoretical expression and published measurements, the fit to experimental results is shown to support the model. Furthermore, the model accounts for much of the data in the literature of the behaviour of this enzyme.