Preparation of fluorescent derivatives of lipases and their use in fluorescence energy transfer studies in hydrocarbon/water interfaces

Fluorescein isothiocyanate reacted with a chromobacter and pseudomonad lipase to yield mono-substituted, fully active, enzymes. With the carbocyanine dye 1,1′-dioctadecyl-3,3,3′,3′-tetramethylindocarbocyanine perchlorate (DiI) in the non-aqueous phase, fluorescence energy transfer was used to follow the lipase and similarly labelled model proteins in and out of the interface in heptane, and heptane/di-O-palmitoyl-rac-glycerol (a substrate analogue), emulsions. Competitive binding, and displacement by other proteins could also be followed.