Binding of Spermidine and Putrescine to Energized Liver Mitochondria

The binding of spermidine and putrescine to mitochondrial membranes was studied by applying a thermodynamic model of ligand–receptor interactions developed both for equilibrium and far-from-equilibrium binding processes (V. Di Noto, L. Dalla Via, A. Toninello, and M. VidaliMacromol. Theory Simul.5, 165–181, 1996). Results demonstrate the presence of two monocoordinated binding sites (S1and S2) for spermidine and one monocoordinated binding site (S2) for putrescine, all exhibiting high capacity and low affinity. It is proposed that differences in the polyaminesʹ flexibility and hydrophilicity perhaps contributes to the observed variations in their interactions with the two sites. A comparison of the binding parameters of these polyamines with those of spermine reveals differences in the specific function of the S1and S2sites, identified in studies of spermine binding (L. Dalla Via, V. Di Noto, D. Siliprandi, and A. ToninelloBiochim. Biophys. Acta1284, 247–252, 1996).