Guanine nucleotides and magnesium dependence of the association states of the subunits of transducin.
When GTP gamma S is bound to transducin (T), the two subunits T alpha X GTP gamma S and T beta gamma dissociate, independently of the ionic environment. When GDP is bound, these subunits are associated as a monomeric T alpha X GDP-T beta gamma complex of 75 kDa when the ionic environment is comparable to that of the cytoplasm, but they dissociate in the presence of 10-100 mM Mg2+ or Ca2+. Using this property, the subunits could be separated and purified by a rapid one-step procedure on an ion-exchange column (FPLC), and their molecular masses were verified by neutron small angle scattering. The physiological relevances of the dissociating effect of Mg2+ are discussed.
D000818:Animals; D002118:Calcium / Q000494:pharmacology; D002413:Cations, Divalent; D002417:Cattle; D055598:Chemical Phenomena; D002627:Chemistry, Physical; D002852:Chromatography, Ion Exchange; D006150:Guanine Nucleotides / Q000378:metabolism*; D006153:Guanosine Diphosphate / Q000378:metabolism*; D006160:Guanosine Triphosphate / Q000378:metabolism*; D046911:Macromolecular Substances; D008274:Magnesium / Q000494:pharmacology*; D008565:Membrane Proteins / Q000378:metabolism*; D009994:Osmolar Concentration; D010786:Photoreceptor Cells / Q000032:analysis*; D011485:Protein Binding; D012374:Rod Cell Outer Segment / Q000032:analysis*; D015293:Transducin
D002413:Cations, Divalent; D006150:Guanine Nucleotides; D046911:Macromolecular Substances; D008565:Membrane Proteins; D006153:Guanosine Diphosphate; D006160:Guanosine Triphosphate; D015293:Transducin; D008274:Magnesium; D002118:Calcium