Spectrofluorimetric study of the intermolecular complexation of monoclonal antibodies with the high potency sweetener N-(p-cyanophenyl)-N'-(diphenylmethyl) guanidineacetic acid.

Molecular complexation between a set of five monoclonal antibodies (MAbs) and a N,N',N"-trisubstituted guanidinium sweetener (TGS) was studied by monitoring the intrinsic fluorescence of the MAbs. Changes in the emission spectral properties of the MAbs were found to be related to the location of tryptophan residues in the antibody complementarity determining regions (CDRs). Two of the MAbs, NC10.10 and NC10.8, showed fluorescence quenching and hypsochromic (blue) shifts in the emission maxima upon complexation with the TGS ligand. Experiments with three other MAbs, NC10.1, NC6.8 and NC2.3, revealed only monotonic fluorescence quenching. The association constants obtained by spectroscopic techniques for the different MAb-TGS complexes were found to be comparable with those determined using a conventional RIA. The thermodynamic parameters of the MAb-TGS complexation were also examined. The intermolecular complexation was found to be exothermic for four of the five MAbs in this study. However, MAb NC2.3 was found to be an exception, in that it was associated with a small positive enthalpic change. This type of spectrofluorimetric analysis can aid in the identification of interactive residues and molecular dynamics involved in TGS recognition by this set of MAb. Such information may prove useful in understanding the molecular recognition motifs responsible for the intense taste properties of high potency guanidine sweeteners.