Conformational features of cell-bound drugs as detected by selective proton relaxation rate investigations.

The nonselective and selective longitudinal relaxation rates were measured for procaine protons in the presence of model lipid membranes, biological membranes and whole cells. Unlike the nonselective relaxation rates, the selective rate was shown to be particularly sensitive in detecting binding interactions with macromolecular cell constituents. It was shown that the aromatic moiety of procaine is involved in binding the cell plasma membrane.