Two protein-biosynthesis inhibitory proteins, luffin-a and -b, were isolated from the seeds of the sponge gourd (Luffa cylindricd). Luffins were extracted from defatted meal of seeds of the sponge gourd with water at pH 4.0 and purified by gel filtration through a Sephadex G-75 column followed by CM-cellulose column chromatography and FPLC with Mono S column. Luffin-a and -b were basic proteins with isoelectric points of about 10, with molecular masses of 28, 000 Da and 29, 000 Da, respectively, as judged by SDS-PAGE. Luffin-a and -b were found to be homologous proteins having similar amino acid compositions (except threonine and proline), and having N-terminal sequences of Asp-Val-Arg-Phe-Ser-Leu-Ser-Gly- and Ala-Asn-Val-Ser-Phe-Ser-Leu-Ser-Gly-, respectively. Inhibitory activities of luffin-a and -b on cell-free protein synthesis were approximately 5.5 and 1.5 fold, respectively, stronger than that of ricin A-chain.

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