Some factors influencing the orientation of ∈-amino groups in monolayers of proteins and amino acid polymers

Abstract

The potentials of monolayers of various proteins and amino acid polymers, including a new synthetic amphoteric amino acid polymer, were measured at the interfaces air-water and oil-water, at pH''s 2, 6.8 and 13. With this new polymer (poly-1, 1,2-L-lysyl-L-glutamyl-L-leucine) all the phenomena shown by protein films can now be reproduced. Other polymers studied were poly-L-lysine, poly-DL-leucine, poly-1,1-gamma-methyl-L-glutamyl-DL-phenylalanine and poly-1,1-DL-lysyl-L-glutamic acid. At pH 13 the un-ionized epsilon-NH2 groups of the lysine residues tend to enter the non-aqueous phase, especially at the air-water interface when the neighboring amino acid residues in the peptide chain are favorable. The "unavailability" of such epsilon-NH2 groups at this interface and in the native protein may be of major biological importance.