Résumé
Lipid digestion is initiated in Human by gastric lipase. Lipolysis of complex lipoproteic assembliessuch as milk fat globules, based on an apolar core of triacylglycerides enveloped by a trilayeredmembrane, is particularly frequent during neonatal digestion1. Such lipolysis proceeds at acid pHand requires a rapid adsorption onto the substrate membrane before the onset of catalyticactivity2. The interactions governing this adsorption are not fully elucidated. Our objective wasthus to unravel these interactions and precise gastric lipase lateral distribution in modelmembranes of milk fat globules presenting liquid phase segregation.Ellipsometry, tensiometry and atomic force microscopy were used to get an insight on theability to the lipase to get inserted into the lipid membrane3. Lipid Langmuir films were used tomimic the outer leaflet of the external membrane of the milk fat globule. Different lipid mixtures ornatural extracts of cow buttermilk with variable physical phases, surface charge and lateralpacking were tailored to identify the nature of the enzyme/membrane interactions. Recombinantdog gastric lipase (rDGL) was used as model of the human gastric lipase.[br/]This combination of biophysical tools indicated that: 1. rDGL is characterized by a highaffinity for the lipid/liquid interface with large amount of molecules located close to the interfacebut limited insertion; 2. rDGL partitions toward liquid expanded phase and at phase boundaries,gets adsorbed at three height levels and strongly impacts on lipid phase lateral organization; 3.besides hydrophobic interactions, rDGL adsorption is favored by electrostatic interactions whichwere investigated through surface potential modelling; addition of local negative charges usingphosphatidylserine reinforced adsorption.The massive amount of gastric lipase located close to the substrate may favor rapidprelipolysis before gastric emptying and subsequent action of pancreatic lipases. Generalizationof this biophysical approach to other digestive lipases to precise their interaction with complexfood substrate is very promising