Review Exploring the specific features of interfacial enzymology based on lipase studies Ahmed Aloulou a,b , Jorge A. Rodriguez a , Sylvie Fernandez a,c , Dirk van Oosterhout a , Delphine Puccinelli a,b , Frédéric Carrière a, ⁎ a Laboratoire d’Enzymologie Interfaciale et de Physiologie de la Lipolyse, CNRS UPR 9025, 31 Chemin Joseph Aiguier, 13009 Marseille, France b Laboratoires Mayoly-Spindler, 6 avenue de l’Europe, 78401 Chatou, France c Gattefossé SAS, 36 chemin de Genas, 69804 Saint-Priest, France Received 19 May 2006; received in revised form 17 June 2006; accepted 27 June 2006 Available online 8 July 2006 Abstract Many enzymes are active at interfaces in the living world (such as in the signaling processes at the surface of cell membranes, digestion of dietary lipids, starch and cellulose degradation, etc.), but fundamental enzymology remains largely focused on the interactions between enzymes and soluble substrates. The biochemical and kinetic characterization of lipolytic enzymes has opened up new paths of research in the field of interfacial enzymology. Lipases are water-soluble enzymes hydrolyzing insoluble triglyceride substrates, and studies on these enzymes have led to the development of specific interfacial kinetic models. Structure–function studies on lipases have thrown light on the interfacial recognition sites present in the molecular structure of these enzymes, the conformational changes occurring in the presence of lipids and amphiphiles, and the stability of the enzymes present at interfaces. The pH-dependent activity, substrate specificity and inhibition of these enzymes can all result from both “classical” interactions between a substrate or inhibitor and the active site, as well as from the adsorption of the enzymes at the surface of aggregated substrate particles such as oil drops, lipid bilayers or monomolecular lipid films. The adsorption step can provide an alternative target for improving substrate specificity and developing specific enzyme inhibitors. Several data obtained with gastric lipase, classical pancreatic lipase, pancreatic lipase-related protein 2 and phosphatidylserine-specific phospholipase A1 were chosen here to illustrate these specific features of interfacial enzymology. © 2006 Elsevier B.V. All rights reserved. Keywords: Lipase; Phospholipase; Colipase; Interfacial enzymology; Enzyme structure; Lipid-protein interaction; Protein adsorption; Lipase inhibitor; PS-PLA1; PLRP2; Gastric lipase; Pancreatic lipase 1. Introduction The field of interfacial enzymology is gradually becoming recognized as a specific field of research, because many enzymes are involved in the processes at work at interfaces in the living world, as well as in biotechnological processes (such as those occurring in cell membranes, at solid surfaces and at oil–water interfaces). This aspect of enzymology is still absent, however, from most general textbooks. One reason for this gap is probably that theoreticians in the field of enzymology have not taken much interest in enzymes acting at interfaces, and usually work with model systems well adapted for a mathematical treatment of experimental data. It is also rather difficult to analyze the experimental data obtained with a soluble enzyme acting on an insoluble substrate because one has to take into account the partitioning of the enzyme between the aqueous phase and the substrate interface. In most experimental set-ups, the enzyme activity and the partitioning processes cannot be measured simultaneously and only ” apparent” kinetic constants can be obtained. One therefore quite commonly reads reports on the K m and k cat of interfacial enzymes such as lipases, although the Michaelis–Menten–Henri model only applies, strictly speaking, to experimental data on soluble enzymes and substrates present in the same phase. Expressing a K m , which has the dimension of a volume concentration, has no meaning with an insoluble substrate. Some chapters on interfacial enzyme kinetics are now becoming available, however [1,2], and our aim here is not to Biochimica et Biophysica Acta 1761 (2006) 995 – 1013 www.elsevier.com/locate/bbalip ⁎ Corresponding author. Laboratoire d'Enzymologie Interfaciale et de Physiologie de la Lipolyse, UPR 9025 CNRS, 31 Chemin Joseph Aiguier, 13402 Marseille Cedex 20, France. Tel.: +33 4 91 16 41 34; fax: +33 4 91 71 58 57. E-mail address: carriere@ibsm.cnrs-mrs.fr (F. Carrière). 1388-1981/$ - see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.bbalip.2006.06.009