Several kinds of shrews produce anesthetic substances which they inject into the bodies of their prey, such as earthworms and insects. The paralyzed prey are then stored in their nest. Due to the interesting ecology of shrews, we sought to isolate these anesthetic substances. We studied the American short-tailed shrew Blarina brevicauda, which produces a potent venom. Despite its classification as an "Insectivore", it consumes not only insects and other invertebrates, but also vertebrates, including prey even larger than itself. Guided by acute toxicity against mice, the extract of its submaxillary gland was separated using column chromatography, and a lethal venom, blarina toxin, and its derivative, blarinasin, were isolated. Mice injected with blarina toxin showed characteristic symptoms, i.e., irregular and quickened respiration, paralysis of the hind limbs, and convulsions before death. The mature form of the primary amino acid sequences of blarina toxin (253 residues) and blarinasin (252 residues) were determined using partial amino acid sequence analysis and cDNA cloning, respectively. Both of these proteins were a type of secretory serine protease. Studies on posttranslational modification and the mode of action of blarina toxin are in progress. We also studied the long-clawed shrew Sorex unguiculatus, which inhabits Hokkaido. Guided by the N-type calcium channel activity, the aqueous extract of its submaxillary gland was subjected to separation using ultrafiltration and column chromatography. Further purification of the active fraction using reversed-phased HPLC is in progress.
