Phospholipid monolayer hydrolysis by cytosolic phospholipase A2 gamma and lecithin retinol acyl transferase

Cell membranes are modified by the action of different types of enzymes. The action of these enzymes is difficult to properly follow when using cells because of the large number of proteins and lipids present in cell membranes. Model membrane systems such as phospholipid monolayers are thus very useful to improve our understanding of the activity of enzymes towards membranes. Phospholipases A2 (PLA2) is a large family of enzymes that hydrolyze the sn-2 fatty acyl chain of phospholipids. Cytosolic PLA2 gamma (cPLA2-γ) is a member of this family and can be found in different tissues. Lecithin retinol acyl transferase (LRAT) is involved in the regeneration of the chromophore of the visual pigment rhodopsin. The first step of its enzymatic activity involves the hydrolyzis of the sn-1 fatty acyl chain of phospholipids. Very little information on the membrane binding and hydrolytic activity of these enzymes is available. Recombinant cPLA2-γ and tLRAT (a truncated form of LRAT) were thus cloned, expressed and purified and measurements of protein binding and phospholipid hydrolysis have been performed in monolayers at the air–water interface.