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A new toxic protein named malanin was isolated from seeds of Malania olei fera by hydrophobic chromatography, whose cytotoxic activities against carcinoma cells were very strong. The conformational changes of malanin at various temperatures, pH, organic solvents, surfactant, denaturant and fluorescence quenching solvents were studied by fluorescence spectra. The fluorescence spectra of malanin excited at 280 nm and 295 nm showed a maximum at 340 nm. The emission spectra of malanin showed that Trp residues were located by a great degree in the hydrophobic area. Addition of SDS, CH5N3 x HSCN, acrylamide and KI led to changes in the molecular conformation of malanin, and caused the fluorescence quenching of Trp residues. The red-shifted emission band of malanin after adding CH5 N3 x HSCN showed that Trp residues were exposed in polar solvents.