Effects of Fe ³⁺ /Fe ²⁺ on Glycation Reaction of β -lactoglobulin

Iron ions (Fe 2+ and Fe 3+ ) are essential trace elements for the human body, and are often added to various foods, but their effects on protein glycation remain unclear. This study evaluated the differential influences of Fe 2+ and Fe 3+ on the glycation reaction of β -lactoglobulin ( β -Lg)-D-ribose system in terms of glycation degree, protein conformation and the distribution of modification sites. Free amino group contents and HPLC HCD MS/MS analyses indicated that both Fe 3+ and Fe 2+ could catalyze the glycation process and increase the glycated sites. The system contain Fe 2+ exhibited higher glycation degree and more glycation sites (8), and lesser glycation sites were identified in system contain Fe 3+ (5) and system without ferric ions (2). Additional sites (L1, K14, K135) were facilitated glycation by Fe 2+ , and most glycation sites showed higher degree of substitution per peptide (DSP) values when with Fe 2+ . In comparison with Fe 2+ , Fe 3+ caused more pronounced alterations on both secondary and tertiary protein structure, promoted the β -Lg unfolding, and changed the protein structure to a more unordered form. In conclusion, Fe 2+ at a specified concentration was a better choice to promote glycation reaction while maintain the protein structure. This study provide a theoretical basis for protein glycation modification with iron ions at different valence states participated.