This paper describes the interaction between 2,4-dinitrophenol (DNP) with the two drug carrier proteins - human serum albumin (HSA) and human holo transferrin (HTF). Hence, binding characteristics of DNP to HSA and HTF were analyzed by spectroscopic and molecular modeling techniques. Based on results obtained from fluorescence spectroscopy, DNP had a strong ability to quench the intrinsic fluorescence of HSA and HTF through a static quenching procedure. The binding constant and the number of binding sites were calculated as 2.3 × 10(11) M(-1) and .98 for HSA, and 1.7 × 10(11) M(-1) and 1.06 for HTF, respectively. In addition, synchronous fluorescence results showed that the microenvironment of Trp had a slight tendency of increasing its hydrophobicity, whereas the microenvironment of the Tyr residues of HSA did not change and that of HTF showed a significant trend (red shift of about 4 nm) of an increase in polarity. The distance between donor and acceptor was obtained by the Förster energy according to fluorescence resonance energy transfer, and was found to be 3.99 and 3.72 nm for HSA and HTF, respectively. The critical induced aggregation concentration (CCIAC) of the drug on both proteins was determined and confirmed by an inflection point of the zeta potential behavior. Circular dichroism data revealed that the presence of DNP caused a decrease of the α-helical content of HSA and HTF, and induced a remarkable mild denaturation of both proteins. The molecular modeling data confirmed our experimental results. This study is deemed useful for determining drug dosage.
Keywords: 2-4-dinitrophenol; CD; HSA; HTF; RLS; fluorescence quenching; molecular modeling; polarized fluorescence; zeta potential.