Protein‐synthesis inhibitory protein from seeds of Luffa cylindria roem

A protein (designated as luffin) with an app. M r of 26000, which inhibits protein synthesis in rabbit reticulocyte lysate, was purified to homogeneity from the seeds of Luffa cylindria roem by extraction with 20 mM Na phosphate buffer (pH 7.2) containing 0.2 M NaCl, ammonium sulfate fractionation, and chromatography on Sephacryl S‐200 and CM‐Sephadex C‐25. Luffin exhibited 10‐times as strong inhibitory activity against protein synthesis in rabbit reticulocyte lysate (IC 50, 0.42 ng/ml) as that of ricin A‐chain, but it showed only a weak cytotoxicity against murine leukemia L1210 cells, an activity of 1/106 to 1/105 that of ricin.