Photocontrol of protein conformation in a Langmuir monolayer

We report a method to control the conformation of a weak polyampholyte (the protein beta -casein) in Langmuir monolayers by light, even though the pro tein is not photosensitive. Our approach is to couple the monolayer state t o a photochemical reaction excited in the liquid subphase. The conformation al transition of the protein molecule is triggered through its sensitivity to a subphase bulk field (pH in this study), changing in the course of the photochemical process. Thus, reaction of photoaquation of the ferrocyanide ion, which increases the subphase pH from 7.0 to about 8.3, produces a chan ge in the surface monolayer pressure, Delta Pi, between -0.5 and +1.5 mN/m (depending on the surface concentration), signalling a conformational switc h. The approach proposed here can be used to selectively target and influen ce different interfacial properties by light, without embedding photosensit izers in the matrix. (C) 2001 American Institute of Physics.