PURIFICATION AND PARTIAL CHARACTERIZATION OF SINGLE-CHAIN RIBOSOME-INACTIVATING PROTEINS FROM THE SEEDS OF PHYTOLACCA-DIOICA L

Three ribosome-inactivating proteins (RIPs) similar to those already k nown (Stirpe et al. (1992) Bio/Technology 10, 405-412) were purified f rom the seeds of Phytolacca dioica. These proteins, called Phytolacca dioica RIPs (PD-S1, PD-S2 and PD-S3 RIPs), are glycoproteins, with M(r ) approx. 30000, inhibit protein synthesis by a rabbit reticulocyte ly sate and phenylalanine polymerization by isolated ribosomes, and depur inate rat liver rRNA in an apparently identical manner as the A-chain of ricin and other RIPs (Endo et al. (1987) J. Biol. Chem. 262, 5908-5 912). Part of the purified rat liver ribosomes appeared resistant to t he action of PD-S RIPs. The most abundant protein, PD-S2 RIP, gave a w eak or nil cross-reaction with sera against various other RIPs, includ ing a pokeweed antiviral protein from the roots of Phytolacca american a. PD-S2 RIP was linked to a monoclonal antibody (Ber-H2) against the CD30 human lymphocyte antigen and the resulting immunotoxin was select ively toxic to the CD30+ Hodgkin's lymphoma-derived L540 cell line.