CHARACTERIZATION OF THE ENZYMATIC MECHANISM OF GAMMA-MOMORCHARIN, A NOVEL RIBOSOME-INACTIVATING PROTEIN WITH LOWER MOLECULAR-WEIGHT OF 11,500 PURIFIED FROM THE SEEDS OF BITTER GOURD (MOMORDICA-CHARANTIA)

The enzymatic mechanism of a small ribosome-inactivating protein, gamm a-momorcharin, purified from the seeds of Momordica charantia, has bee n characterized. By SDS-polyacrylamide and electrospray ionization mas s spectrometry, its molecular weight was measured to be 11,500 daltons which is much lower than other RIPs known to date. It can inhibit the protein synthesis in the rabbit reticulocyte cen-free system with ID5 0 of 55 nM. When rat liver ribosome was incubated with gamma-momorchar in, a diagnostic RNA fragment appeared on the gel after rRNAs were tre ated with acid aniline. Sequencing of the RNA fragment indicates that the action site of gamma-momorcharin in 28S ribosomal RNA of rat liver is at a specific adenosine (position 4324), which is in a highly cons erved loop of 28S rRNA. (C) 1996 Academic Press, Inc.