The nature of the EGCG-LR peptide interactions.

<p>Electrospray ionization mass spectrum of peptide (<b>A</b>) or peptide-EGCG mixture (<b>B, C</b>). The peptide solution was prepared by incubating each peptide (5 µM) with or without EGCG (5 µM) in water at room temperature for 15 min. Solutions of the mixture were analyzed in the positive ion mode. The arrows in the figure show the observed ion peaks. <b>A</b>) The Cys residue-containing peptide human LR161-170 and (<b>B</b>) its mixture with EGCG. <b>B</b>) An inset is the figure zooming in the relevant peak to see the difference between non-covalent (<i>m/z</i> 749.7 [LR161-170+EGCG+2H]²⁺) and covalent binding (<i>m/z</i> 748.7 [(LR161-170+EGCG-2H)+2H]²⁺). <b>C</b>) Mass spectrum of the mixture of the Cys residue-lacking peptide soy LR168-177 with EGCG. [LR161-170+2H]²⁺ or [Soy LR168-177+2H]²⁺ represents the doubly protonated form of each peptide. [LR161-170+EGCG+2H]²⁺ or [Soy LR168-177+EGCG+2H]²⁺ represents the peptide ion with added EGCG (EGCG-peptide complexes).