(-)-
Epigallocatechin gallate (EGCG) is a major bioactive component in leaves of
green tea, and has been widely investigated for its anti-
tumor activity. The interaction between EGCG and the key
peptides or
proteins (e.g.
glutathione,
enzymes) in vivo is thought to be involved in the toxicity and anti-
cancer mechanism of EGCG. However, the true anti-
tumor mechanism of EGCG is not clear, and few studies have focused on the reactivity of EGCG toward
peptides or
proteins under physiological conditions (pH 7.4, 37 degrees C). In this work, the covalent interactions between EGCG and model
peptides containing one or more nucleophilic residues (i.e. Arg, Cys, Met, and alpha-NH(2) of the N-terminus of
peptides) under physiological condition were fully characterized using mass spectrometry. It was found that EGCG can react with the
thiol groups of
peptides to form adducts under physiological conditions (pH 7.4, 37 degrees C), even in the absence of the
peroxidase/
hydrogen peroxide system. Besides the
thiol groups of
peptides, it is firstly reported that EGCG also reacts with alpha-NH(2) of the N-terminus or
arginine residues of model
peptides to form
Schiff base adducts, and the
methionine residues of model
peptides can be easily oxidized by
hydrogen peroxide (H(2)O(2)) generated during the process of EGCG auto-oxidation to form
methionine sulfoxide products. The preference for the reaction of nucleophlic residues of
peptides with EGCG was determined to have the following order: Cys > alpha-NH(2) of the N-terminus > Arg. The neutral loss
ions of [M+H-170](+) and [M+H-138](+) were detected in all tandem mass spectra of the EGCG adducts of
peptides, which indicates that these two neutral loss
ions can be considered as the characteristic neutral loss
ions of
peptides modified by EGCG. Results of the present research provide insights into the toxicology and anti-
tumor mechanism of EGCG in vivo.