The exchange properties of magnesium in Escherichia coli ribosomes

Although some work has been done on the metabolism of the RNA and, to a lesser extent, of the protein in ribosomal particles The general physical characteristics of Escherichia coli ribosomes have been studied by Tissieres, Watson, Schlessinger & Hollingworth (1959), of yeast ribosomes by Chao & Schachman (1956), of peaseedling ribosomes by Ts'o, Bonner & Vinograd (1958) and of rat-liver ribosomes by Petermann, Hamilton, Balis, Samarth & Pecora (1958). The importance of magnesium in the structure of these particles is well known, and the dissociation of larger into small sub-units when magnesium is removed from them appears to be a general feature (Tissieres et al. 1959; Bolton, Hoyer & Ritter, 1958; Chao, 1957). Protein has also been implicated in this association (Morgan, Greenspan & Cunning- ham, 1963). Little attention has been paid to the properties of the magnesium bound to and involved in the structure of ribosomes. The binding of magnesium to Jensen-sarcoma ribosomes has been investigated by The exchange between free Mg2+ ions and rabbit-reticulocyte-microsomal magnesium has been studied by Edelman, Ts'o & Vinograd (1960), who found that 100 % of the microsomal magne- sium exchanged in about 30 min.