In differentiating keratinocytes, fusion of lamellar body (LB) membranes with the plasma membrane enriches the plasma membrane with lipids including omega-OH-ceramides. Their fatty acid chains are long enough to span the lipid bilayer, so that the omega-OH projects into the cell. In vitro data have shown that the membrane-anchored transglutaminase 1 enzyme can covalently esterify these ceramides onto glutamine residues of cornified envelope scaffold proteins (Nemes et al. 1999). Eventually, the ceramides replace the bilayer plasma membrane and are thought to serve to interdigitate with and organize the extracellular lipids into characteristic lamellae (Kalinin et al. 2001).