The exchange properties of magnesium in Escherichia coli ribosomes

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Abstract
The structure of E. coli ribosomes was investigated by ultra-centrifugation, dialysis and Mg28 exchange. About 35% of the Mg in the 70s ribosomes exchanges in less than 2 min. at 0[degree]. Mg in the 50s particles exchanges at 5-6%/hr., and that in a mixture of 50s and 30s ribosomes at 3-4%/hr. Dialysis experiments show that 35% of the 70s ribosomal Mg is involved in association of the subunits. The rapidly exchanging Mg in 70s ribosomes is that associated with the formation of 70s ribosomes from the subunits. Dialysis of 50s ribosomes against tris buffer free of Mg2+ ions suggests that two 30 ribosomes are involved in the structure of the 50s ribosome. Tris buffers made 1-10 m[image] with respect to Mg2+ ions is not essential for the observation of 70s ribosomes in crude extracts of E. coli. Substantial quantities of 70s ribosomes are observed in extracts in tris buffer made 0-1 m[image] with respect to Mg2+ ions if these extracts are made by grinding with alumina but not by shaking with glass beads.