SPERMINE BINDING TO SUBSYNAPTOSOMAL FRACTIONS OF RAT-BRAIN CORTEX

Binding sites for [14C]spermine have been identified in rat brain cortex subcellular fractions. The binding, characterized by using synaptosomal membranes, is specific for spermine. It was not detected below 20\ub0C and increased about three/four-fold with a temperature rise of 10\ub0C. Binding occurred only in the presence of-SH reducing agents. It was completely suppressed by metal chelating agents, and was stimulated about four-fold by 1-5 710-5 M Fe2+. Smaller increases were observed in the presence of Mn2+, Ni2+, Ca2+, Mg2+, and Zn2+; in ocntrast, millimolar concentrations of most divalent cations inhibited the binding differently (Mn2+=Ni2+=Zn2+=Co2+ 6bMg2+>Ca2+). Bound radioactive spermine was not displaced by the addition of high concentrations of unlabelled polyamine or chelating agents, nor by precipitation and washing of the membranes with 10 percent trichloroacetic acid, or by boiling of the precipitate in the presence of 1.0 percent SDS and 10 percent \u3b2-mercaptoethanol. The trichloroacetic acid precipitate showed two radioactive bands, corresponding to low Mr (