Enzyme--substrate interaction in lipid monolayers. III. A study of the variation of the surface concentration with lipolysis.

Monolayers of a diacylglycerol were submitted to the action of lipase, keeping the area constant. The variation of lipase, keeping the area constant. The variation of the surface concentration gamma of the substrate with time was derived from the recorded reduction of the surface pressure pi (the isotherm of the monolayer being previously established). The rate -d gamma/dt was determined both as a function of the surface concentration gamma of the substrate and as a function of the bulk concentration C of the enzyme in the underlying solution. The rate depends on the quantity of enzyme ze adsorbed on the monolayer and on the enzymatic specific activity alpha of these adsorbed enzyme molecules. Both ze and alpha vary with gamma. The two variations have been quantitatively dissociated. The curves of ze and of alpha as functions of gamma coincide with those previously established in the study of hydrolysis under constant surface pressure.