title: Human serum albumin as an antioxidant in the oxidation of (-)-epigallocatechin gallate: participation of reversible covalent binding for interaction and stabilization.
abstract: Human serum albumin (HSA) contributes to the stabilization of (-)-epigallocatechin gallate (EGCg) in serum. We characterize in the present study the mechanisms for preventing EGCg oxidation by HSA. EGCg was stable in human serum or buffers with HSA, but (-)-epigallocatechin (EGC) was unstable. We show by comparing EGCg and EGC in a neutral buffer that EGCg had a higher binding affinity than EGC. This indicates that the galloyl moiety participated in the interaction of EGCg with HSA and that this interaction was of critical importance in preventing EGCg oxidation. The binding affinity of EGCg for HSA and protein carbonyl formation in HSA were enhanced in an alkaline buffer. These results suggest the reversible covalent modification of EGCg via Schiff-base formation, and that the immobilization of EGCg to HSA, through the formation of a stable complex, prevented the polymerization and decomposition of EGCg in human serum.
authors.affiliation: Department of Food and Nutritional Sciences, and Global Center of Excellence Program, University of Shizuoka, 52-1 Yada, Suruga-ku, Shizuoka 422-8526, Japan. ishii_t@u-shizuoka-ken.ac.jp
authors.forename: Takeshi
authors.initials: T
authors.lastname: Ishii
authors.forename: Tatsuya
authors.initials: T
authors.lastname: Ichikawa
authors.forename: Kanako
authors.initials: K
authors.lastname: Minoda
authors.forename: Koji
authors.initials: K
authors.lastname: Kusaka
authors.forename: Sohei
authors.initials: S
authors.lastname: Ito
authors.forename: Yukiko
authors.initials: Y
authors.lastname: Suzuki
authors.forename: Mitsugu
authors.initials: M
authors.lastname: Akagawa
authors.forename: Kazuki
authors.initials: K
authors.lastname: Mochizuki
authors.forename: Toshinao
authors.initials: T
authors.lastname: Goda
authors.forename: Tsutomu
authors.initials: T
authors.lastname: Nakayama
mesh_terms: D000332:Aerobiosis; D000586:Amination; D000975:Antioxidants / Q000378:metabolism*; D002392:Catechin / Q000031:analogs & derivatives* / Q000737:chemistry / Q000378:metabolism; D006801:Humans; D010084:Oxidation-Reduction; D011485:Protein Binding; D011748:Pyrogallol / Q000737:chemistry / Q000378:metabolism; D012709:Serum Albumin / Q000378:metabolism*; D014867:Water / Q000737:chemistry
chemical_list: D000975:Antioxidants; D012709:Serum Albumin; D011748:Pyrogallol; D014867:Water; D002392:Catechin; C045651:epigallocatechin gallate; C057580:gallocatechol