Activation of many membrane proteins requires a conformational transition induced by specific binding of a small molecule agonist to well-defined sites.  The time dependence of the resulting protein activity is often far more complex than can be rationalized by a kinetic scheme involving only a few protein states.  A mechanism is considered in which agonist can also modulate protein activity by adsorbing to the bilayer in which the protein is embedded, altering key physical properties of the bilayer, and thus distorting the protein conformational free energy landscape.  The complexity of the predicted activity arises from the time-dependence of solute adsorption and desorption, which results in time-dependent rate ''constants'' of transitions between protein conformational states.