title: Quantitation of cation binding to wheat germ ribosomes: influences on subunit association equilibria and ribosome activity.
abstract: The binding of Mg2+, spermine, and spermidine to wheat germ ribosomes was quantitated following equilibrium dialysis. The Mg2+ binding data demonstrate that Mg2+ and K+ compete for binding to the ribosomes. Mg2+ binding saturates at approximately 0.56 positive charges per phosphate (+/P). The Mg2+, spermine and spermidine binding data indicate that either polyamine replaces Mg2+ upon binding to the ribosomes. Mg2+ and polyamine binding combined saturates at approximately 0.29 +/P under the conditions reported. When a critical number of Mg2+ ions are replaced by either polyamine, the activity of the ribosomes falls dramatically. Ribosomal subunit association increases with the degree of phosphate charge neutralization due to the binding of Mg2+. Total charge neutralization during subunit association by Mg2+ and polyamine binding combined, is much less than that achieved by Mg2+ alone.
mesh_terms: D002412:Cations / Q000378:metabolism*; D003956:Dialysis; D008274:Magnesium / Q000378:metabolism; D010649:Phenylalanine / Q000378:metabolism; D014176:Protein Biosynthesis; D012270:Ribosomes / Q000378:metabolism* / Q000648:ultrastructure; D013095:Spermidine / Q000378:metabolism; D013096:Spermine / Q000378:metabolism; D014908:Triticum
chemical_list: D002412:Cations; D013096:Spermine; D010649:Phenylalanine; D008274:Magnesium; D013095:Spermidine