Enzymatic reactions in liposomes using the detergent-induced liposome loading method

Microcompartmentalization is a crucial step in the origin of life. More than 30 years ago, Oparin et al. proposed models based on biochemical reactions taking place in so-called coacervates. Their intention was to develop systems with which semipermeable microcompartments could be established. In the present work we follow their intuition, but we use well-characterized bilayer structures instead of the poorly characterized coacervates. Liposomes from phospholipids can be used as microreactors but they exhibit only a modest permeability and, therefore, chemical reactions occurring inside these structures are depleted after a relatively short period. Here it is shown that even highly stable liposomes from 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) can be used as semipermeable microreactors when treated with sodium cholate. Using this kind of mixed liposomes, we describe a biochemical reaction occurring inside the liposomes while the same reaction is prevented in the external medium. In addition, we show that this cholate-induced permeability of POPC bilayers can even be used to load macromolecules such as enzymes from the outside.