Monolayers of Some Cyclic Peptides. Fungisporin and Gramicidin J1

Abstract

Abstract Monolayers of two naturally occurring cyclic peptides, fungisporin and gramicidin J1, were investigated by the measurements of surface pressure, potential, and viscosity. Fungisporin, an octapeptide composed of phenylalanyl and valyl residues, gave a monolayer of a condensed type. Gramicidin J1, an electrolytic heptapeptide containing a prolyl and two ornithyl residues, gave an unionized monolayer of an expanded type on an alkaline subphase. It behaved in a somewhat specific manner when neutral salt such as potassium chloride was present. The configurations of these cyclic peptides in monolayer were suggested in such a way as intramolecular hydrogen bonding could cause a maximum number of seven-membered rings. Then fungisporin can take four possible square-like configurations, which are equally probable, and gramicidin J1 can take two possible configurations. When these configurations of both peptides are put on surfaces, side chains of all the d-residues always orientate oppositely to those of all the l-residues with respect to the surfaces. In taking account of the condensation and expansion of these monolayers, together with those of tyrocidine A and B and gramicidin SA, it was concluded that cyclic peptides give more condensed monolayers as the contents of prolyl residue are higher. Thus a prolyl residue plays the same role in cyclic peptides as in linear polypeptides. Gramicidin J1 gave a monolayer of more expanded type on a neutral subphase, and exhibited a characteristic behavior common with ionized monolayers when neutral salt such as potassium chloride was added. At very large areas the the behavior was adequately explained by the theory of the electric double layer, when only one ionized residue was assumed to concern the double layer.