Figure 2

The calcium displacement technique. The β-radiation emitted from ⁴⁵Ca²⁺ ions in an aqueous subphase is shielded by the aqueous layer above the ions, yielding the β-intensity I _sub . (2.) A monolayer prepared on the subphase leads to the adsorption of calcium and in particular of ⁴⁵Ca²⁺ ions to the surface, and subsequently a higher β-radiation I _tot can be detected. The β-intensity resulting from the monolayer can be calculated as I _mono = I _tot - I _sub . (3.) Substances having a higher affinity to the lipid monolayer as compared to Ca²⁺ lead to the displacement of the Ca²⁺ ions from the surface and a reduction of the β-intensity I _tot . The titration of peptides/proteins into the buffer can lead to a time trace of the β-intensity as depicted exemplarily in the lower trace.