The diffusion of glycine and N-substituted glycines across bimolecular lipid membranes

Free glycine was shown to diffuse very slowly across synthetic bimolecular lipid membranes, whereas several N-substituted derivatives of glycine were found to penetrate the membranes more readily. Pyridoxal, formaldehyde and acetaldehyde were shown to enhance the diffusion of glycine across the membranes, presumably the result of imine formation between the aldehyde and the α-amino group of glycine. Several N-substituted glycines were synthesized and their rates of efflux from liposomes were found to be related to their water-chloroform partition coefficients. This is the first demonstration of carrier-mediated diffusion of amino acids across bimolecular lipid membrane.