AMINO-ACID-SEQUENCES AND RIBOSOME-INACTIVATING ACTIVITIES OF KARASURIN-B AND KARASURIN-C

Complete amino acid sequences of karasurin-B and karasurin-C purified from root tubers of Trichosanthes kirilowii MAXIM. var.japonica KITAMU RA (Cucurbitaceae) were determined. Karasurin-B consists of 247 amino acid residues with a calculated molecular weight of 27214 Da and karas urin-C of 249 amino acid residues with a calculated molecular weight o f 27401 Da. Their amino acid sequences are quite similar to that of ka rasurin-A, a major basic protein from the same root tubers, but the pi values are slightly different among them. All karasurins strongly inh ibited in vitro translation in the rabbit reticulocyte system. The ami no acid sequences of karasurins were compared with those of the riboso me-inactivating proteins (RIPs) from nine different species by UPGMA m ethod, and the RIPs from Cucurbitaceae plants phylogenetically formed one cluster clearly distinguishable from those of other origin.