Analogues of latarcins Ltc1 and Ltc3b, antimicrobial peptides from the venom of the Central Asian spider Lachesana tarabaevi capable of formation of amphiphilic structures in membranes without involvement of disulfide bonds, were synthesized. The amino acid sequences of the analogues correspond to immature forms of these peptides, each of them containing an additional C-terminal amino acid residue. It is concluded from the study of the biological activity of the synthesized peptides that the posttranslational C-terminal amidation of Ltc3b is a functionally important modification that ensures a high activity of the mature peptide. The lipid composition was shown to affect the interaction of synthesized peptides with artificial membranes. The analogue of Ltc3b manifested the highest activity on cholesterol-containing membranes. The mechanism of action of the studied antimicrobial peptides on membranes is discussed. © 2007 Pleiades Publishing, Inc.