Pit viper venom is haemotoxic but opossums have a blood protein, the von Willebrand Factor (vWF), which improves the animal’s ability to neutralise the anti-coagulant effect of the venom. In the 1990s researchers isolated the peptide from the opossum protein that was responsible for the effect. In a PLoS One article1 published in 2011, DNA researchers noted a sort of evolutionary arms race whereby the venom gene evolved by rapid mutation while the opossum’s immunity kept pace by unexpectedly high rates of replacement substitutions in the specific amino acids in vWF that interact with toxin proteins.
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