Dodecandrin, a new ribosome-inhibiting protein from Phytolacca dodecandra

Dodecandrin, a newly discovered ribosome-inhibiting protein, has been isolated and purified from the leaves of the African endod plant, Phytolacca dodecandra. Dodecandrin has a molecular weight of approx. 29 000. It cross-reacts with antiserum prepared against pokeweed antiviral protein from Phytolacca americana and exhibits similar requirements for antiribosomal activity. It is more basic than pokeweed antiviral protein, and comparison of the first 30 amino-terminal residues of the two proteins reveals 83% homology. This level of homology is greater than that between pokeweed antiviral protein and pokeweed antiviral protein S, another antiviral protein found in P. americana. Such conservatism in sequence, coupled with the high efficiency of the proteins in deactivating ribosomes and with their abundance in plant tissue, suggests that they serve an important function in the life of the plant, probably as a defense against infection.