A novel cytotoxic protein, Karatoxin, from the dorsal spines of the redfin velvetfish, Hypodytes rubripinnis

A novel cytotoxic protein from the dorsal spines of the redfin velvetfish, Hypodytes rubripinnis, was isolated by a combination of affinity chromatography techniques. The 110-kDa glycoprotein is named Karatoxin. The N-terminal partial amino acid sequence of intact 76-kDa sub-unit of Karatoxin was analyzed as follows: DQHDDxPxxAPDPG. The 76-kDa sub-unit was determined to have mannose moieties. Karatoxin exhibited cytotoxic activity on murine P388 leukemic cells. Furthermore, Karatoxin induced mitogenic stimulation on murine splenocytes. These results suggest that the redfin velvetfish, H. rubripinnis, may be a novel resource for biologically active substances.