Interactions of Divalent Cations Affecting Polyribosomal Profiles from Paramecium—With Particular Reference to the Interactions of Strontium with Calcium, Magnesium, and Manganese
The role of monovalent and divalent cations on stabilizing ribosomal material— and to a lesser extent polyribosomal material—in prokaryotes and higher eukaryotes has been the subject of considerable study in the past (see ref. 1 for earlier references). More recently Jackson and Larkins (2) reported on the effect of ionic strength, pH, and the chelation of divalent cations using ethyleneglycol-bis(2-aminoethyl ether) tetraacetic acid (EGTA) when isolating polyribosomes from tobacco leaves. They found that the use of EGTA (which has a high affinity for Ca2+, Cu2+, and Zn2+) significantly increased the yield of polyribosomal material, particularly from expanded leaves, while at the same time increasing the proportion of what appears to be 60 S material at the expense of the 80 S ribosomal zone. Furthermore, by using material from unexpanded leaves, which yields quite reasonable amounts of polyribosomes without the use of EGTA, they could greatly reduce the yield by introducing 25 mM Ca2+, Cu2+, or Zn2+. The overall shape of the profiles, however, i.e., the relative proportions of different classes of polyribosomes to one another, appears to have remained unchanged. Earlier, Larkins and Davies (3) reported that Ca2+ caused degradation of polyribosomes extracted from peas by RNAase activation, but this was not found to occur in tobacco leaves, nor have we found any indication of RNAase activation by Ca2+ in the Paramecium system.
KeywordsDensity Gradient Divalent Cation Homogenize Medium Monovalent Cation Sucrose Density Gradient
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