Exploring the fluorescence quenching interaction of amino acids and protein with natural organic matter by a multi-spectroscopic method

Abstract

The main objective of this research was to explore the fluorescence quenching mechanism of a humic substance (Suwannee River natural organic matter (SWNOM)) to amino acids (tryptophan, tyrosine) and protein (bovine serum albumin, (BSA)) by multi-spectroscopic methods. The locations of the peaks of tryptophan, tyrosine, and BSA from Parallel Factor Analysis were at Ex/Em 280/356 nm, 275/302 nm, and 280/344 nm, respectively. For SWNOM, two peaks appeared at Ex/Em of 240/448 nm, and 350/450 nm. Static quenching was the dominant quenching mechanism between BSA and SWNOM, whereas no quenching was observed between tryptophan or tyrosine and SWNOM. Fourier-transform infrared spectroscopy and thermodynamic calculation demonstrated that hydrogen bonding and van der Waals force are the potential binding forces of the BSA-SWNOM complex, as a result of rearrangement in the secondary polypeptide carbonyl hydrogen bonding network of BSA. This rearrangement led to the conformational change in BSA that induced quenching of BSA fluorescence by SWNOM. HIGHLIGHTS No quenching of tyrosine and tryptophan by Suwannee River natural organic matter (SWNOM).; Quenching of bovine serum albumin (BSA) by SWNOM occurs only when BSA is in the tertiary structure.; FTIR amide I peak of BSA was shifted on the addition of SWNOM.; Non-covalent bonding forms and quenching is static between BSA and SWNOM.;

Keywords

• bovine serum albumin
• fluorescence quenching
• fluorescence titration
• parafac
• tryptophan
• tyrosine