ABSTRACT:
Many plants accumulate proteins that are commonly referred to as ribosome-inactivating proteins (RIPs). Biological effects described to these proteins go back to ancient times because of the high toxicity of seeds of castor bean (Ricinus communis) and jequirity bean (Abrus precatorius), as well as anti-HIV, the abortifacient activity of some plants like Trichosanthes kirilowii and Momordica charantia, rely on the presence of RIPs. Pokeweed antiviral protein, and ricin, previously described as ribosome-inactivating proteins were shown to damage single-stranded DNA by removal of a protein-specific set of adenines. RIPs are enzymes and some have multiple enzymatic activities. These enzymes are expected to damage DNA rather than participate in repair processes. All RIPs depurinated DNA extensively and some released adenine from all adenine-containing polynucleotides. The entire class of plant proteins, called ribosome-inactivating proteins, may be classified as polynucleotide: adenosine glycosidases. The significance of this DNAase activity to the biological function of these plant proteins along with their toxicity effect to animal cells remains to be fully understood.