Isolation and characterization of a novel ribosome-inactivating protein, β-kirilowin, from the seeds of Trichosanthes kirilowii

A novel ribosome-inactivating protein designated β-kirilowin was isolated from the seeds of Trichosanthes kirilowii. The proteins exhibited strong abortifacient activity in pregnant mice and produced a single band after SDS-polyacrylamide gel electrophoresis with an apparent mol. wt. of 27,500 daltons. It was active in inhibiting the cell-free translation system with an ID₅₀ of about 1.8 ng/ml. No cross-reactivity with trichosanthin could be detected by immunodiffusion. Sequence comparison of the first 10 residues of β-kirilowin with ribosome-inactivating proteins isolated from T. kirilowii such as trichosanthin, trichokirin and karasurin indicated 70%, 60% and 70% identity, respectively.