We introduce new nanometer-sized bioreactors based on liposomes functionalized by incorporated natural channel proteins. Additionally the lipid bilayers of the underlying liposomes can be stabilized by a crosslinking polymerization of hydrophobic methacrylate monomers in the interior of the membranes. As a representative example we functionalize (polymer-stabilized) 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphcholine liposomes by reconstituting a channel-forming protein from the outer cell wall of Gram-negative bacteria. The protein used (OmpF) acts as a size-selective filter, which allows only passage of molecules with a molecular weight below 400 g mol(-1). Substrates below this size may still have access to enzymes encapsulated in the nanocontainers. We demonstrate this using the enzyme beta -lactamase, which is able to hydrolyze the antibiotic ampicillin. Interestingly the enzyme and the membrane channel preserve their activity even in the presence of the hydrophobic methacrylate monomers and after their cross-linking polymerization.