Comparison of binding interactions of lomefloxacin to serum albumin and serum transferrin by resonance light scattering and fluorescence quenching methods.

The interaction between lomefloxacin (LMF) and two drug carrier proteins, human serum albumin (HSA) and serum transferrin (TF), were studied and compared by fluorescence quenching, resonance light scattering (RLS), and circular dichroism (CD) spectroscopic along with molecular modeling. Fluorescence data show that LMF has a stronger quenching effect on HSA than on TF. The binding constant and the number of binding sites were calculated as 6.00 x 10(5) M(-1) and 0.77 for HSA, and 4.66 x 10(5) M(-1) and 1.02, for TF, respectively. Also, these binding parameters were calculated by RLS data, as a novel approach and were compared to that obtained from fluorescence. The micro-environment changes of Trp residues were evident in both proteins. The quantitative analysis of the secondary structure in both proteins further confirmed the drug-induced conformational changes. The distance (r) between donors (HSA and TF) and acceptor (LMF) were obtained by fluorescence resonance energy transfer (FRET) theory and found to be 1.83 nm and 1.71 nm for HSA and TF respectively. Moreover, molecular modeling studies suggested the sub-domain IB in HSA and N-lobe in TF as the candidate place for the formation of the binding site of LMF on these proteins.