‘Interfacial activation’ of lipases: facts and artifacts

An important aspect of lipolytic enzymes is the unique physicochemical character of the reactions they catalyse at lipid-water interfaces, involving interfacial adsorption and subsequent catalysis sensu stricto . Lipases are now used as catalysts in aqueous as well as low-water media and accept various molecules as substrates. They were previously defined in kinetic terms, based on ‘interfacial activation'. This phenomenon was not found among esterases. Recently determined 3D structures of some, but not all, upases show a ‘lid' controlling access to the active site. Thus, the presence of a lid, and ‘interfacial activation', are unsuitable criteria for classifying specific esterases. Consequently, lipases can be pragmatically redefined as carboxyl-esterases acting on long-chain acylglycerols: they are simply fat-splitting ‘ferments'.