The hemolytic activity of six arachnid cationic peptides is affected by the phosphatidylcholine-to-sphingomyelin ratio in lipid bilayers.

The hemolytic activity of six cationic amphipathic peptides (Oxki1, Oxki2, Pin1, Pin2, IsCT1 and IsCT2) from arachnids strongly depends on the source of red blood cells. The hemolytic activity of the amphipathic peptides was correlated to the phosphocholine-to-sphingomyelin ratio (PC/SM) content, the potency order of which on mammal erythrocytes ranked as follows Guinea pig>pig>sheep. The spider peptides, Oxki1 and Oxki2, prefer small unilamellar vesicles (SUV) composed of PC, but they could not disrupt SUVs made of SM only. Moreover, the membrane-disrupting activity of the scorpion peptide Pin1 was affected by increasing concentrations of SM. Only the scorpion hemolytic peptide Pin2 was able to disrupt SUVs composed merely of SM at high concentrations. Finally, the short scorpion peptides IsCT1 and IsCT2 seem to tolerate high concentrations of SM in the presence of PC for disruption of SUVs; however, the disrupting activities of IsCT1 and IsCT2 are much lower than that of the other four hemolytic peptides. The hemolytic activity caused by all six cationic peptides in mammalian erythrocytes was positively correlated to increases in temperature and increases in the concentration of benzyl alcohol, a membrane fluidizing agent. It was concluded that the hemolytic activity of the cationic peptides strongly depends on the PC/SM content of mammalian erythrocytes, in which cell membranes with a low PC/SM ratio (i.e., of low fluidity) were less disturbed than membranes with a high PC/SM ratio (i.e., of high fluidity).