Silver Plated Ribosomes

WE recently reported that dissociation of free 70S ribosomes from E. coli to 30S and 50S subunits could occur during sedimentation in buffer containing K⁺ as the predominant monovalent cation¹. Spermidine at a physiological concentration (1 mM) specifically prevented the dissociation and we suggested that the dissociation that occurred in its absence was due to loss of the polyamine from the 70S ribosome. We have subsequently found that this hypothesis is wrong and that the dissociation that took place in the original experiments was due not primarily to loss of spermidine, but to a reaction with silver present in very small amounts in the AR KCl used in the buffer.