Temporal behavior of abrin in the intoxication of Chinese hamster cells (line CHO)

Abrin, a potent cytotoxin, was utilized as a probe to elucidate the mechanism by which external proteins are delivered to the cytoplasm of mammalian cells. Abrin bound rapidly to the surface receptors of the Chinese hamster cells (line CHO) and appeared to be internalized immediately without any significant lag. The maximum level of abrin internalization was achieved within eight minutes, based on both biochemical and electron microscopic autoradiographic studies with [125I]abrin. About 10% of the silver grains of internalized [125I] abrin were associated with vesicular structures, irrespective of the incubation time. Inhibition of protein synthesis began 30 minutes postincubation, and this latent period was not dependent on extracellular toxin concentration. SDS-polyacrylamide gel electrophoresis of the internalized [125I]abrin indicated that internalized abrin molecules remained intact even after two hours of incubation.