Review of binding methods and detection of Al(III) binding events in trypsin and DL-DPPC liposomes by a general thermodynamic model

In this paper are reviewed some of the most useful binding formalisms which have been developed in order to investigate the diversity of the commonly encountered receptor-ligand systems. Particularly, our attention is focused on the presentation and application of a general and rigorous thermodynamic treatment which explains in a simple and coherent way the non-linear profiles observed in the experimental binding, Scatchard, Hill and Adair plots. By applying this model, both qualitative and detailed quantitative investigations were carried out on the binding process of Al(III) to trypsin and DL-dipalmitoylphosphatidylcholine (DPPC) liposomes. Particularly, it has been demonstrated that: Al(III) interacts with liposomes in two binding sites with very different dissociation constants. The first one has been calculated to be 0.0168 mumol l(-1) and the second 2.833 mumol/L. The first is referred to the preferential interaction of Al3+ with the polar head of the phospholipid, while the second most likely regards the interaction of Al3+ with other peripheral sites. On the other hand, Al3+ interacts with trypsin in two types of binding sites. The first binding site with K-1,K-1 = 0.2531 mumol/L and the second with K-2,K-1 = 1.424 mumo/L