ALPHA-KIRILOWIN, A NOVEL RIBOSOME-INACTIVATING PROTEIN FROM SEEDS OF TRICHOSANTHES KIRILOWII (FAMILY CUCURBITACEAE) - A COMPARISON WITH BETA-KIRILOWIN AND OTHER RELATED PROTEINS

A novel ribosome-inactivating protein (RIP) designated alpha-kirilowin was isolated from the seeds of Trichosanthes kirilowii. The molecular weight of alpha-kirilowin was estimated by SDS-polyacrylamide gel ele ctrophoresis to be 28 800 Da, which is slightly larger than another pr eviously characterized ribosome-inactivating protein, beta-kirilowin. The amino-acid composition of alpha-kirilowin grossly resembled beta-k irilowin and other ribosome-inactivating proteins isolated from T. kir ilowii tissues, including trichokirin, trichosanthin and kara-surin. I ntense immunological cross-reactivity between the two kirilowins was d etected by immunodiffusion. The N-terminal sequence of alpha-kirilowin was identical to that of beta-kirilowin, at least in the first ten re sidues. Peptide fingerprinting indicated both kirilowins were closely related. Biological activities as determined by inhibition of protein synthesis in a cell-free system, suppression of [H-3]-thymidine incorp oration into mouse melanoma cells and induction of abortion in mice we re very similar for both kirilowins. We propose that the size differen ce between alpha- and beta-kirilowin is either due to a C-terminal ext ension in alpha-kirilowin or differences in glycosylation, or a combin ation of both. (C) Munksgaard 1996.