Oxytoxins (OxyTx1 and OxyTx2) are disulfide-rich peptides isolated from the venom of the spider Oxyopes lineatus that block voltage-sensitive calcium ion channels (VSCCs). OxyTx1 was identified previously and isolated from the related spider Oxyopes kitabensis; however, its pharmacology was unknown. OxyTx1 and OxyTx2 contain 69 and 55 amino acid residues with molecular masses of 8058.2 and 6175.2 Da, respectively. Oxytoxins contain five disulfide bridges, are amidated at their C-terminus, antagonize P/Q-, N- or L-type VSCCs, and have low amino acid identity to known VSCC blockers from arthropod venoms. OxyTx1 is not specific for VSCCs subtypes when compared to the classical P/Q-type blocker omega-AgaIVA, but OxyTx1 has higher paralytic activity towards Spodoptera litura larvae. Because of their structural and biochemical characteristics OxyTx1 and OxyTx2 may represent a new family of insecticidal peptides. (C) 2008 Elsevier Ltd. All rights reserved.