title: Nanoparticulate glutathione peroxidase mimics based on selenocystine-pullulan conjugates.
abstract: We synthesized nanoparticulate glutathione peroxidase (GPx) mimics in which selenocystine (SeCyst) was conjugated to a hydrophilic linear polysaccharide, pullulan (Pul). The SeCyst ester-conjugated Pul derivatives (SeCyst-Pul) in phosphate buffer (pH 7) were treated with a sonicator to spontaneously form particulate materials. Dynamic light scattering measurements revealed that the SeCyst-Pul conjugates could form particulate materials with diameters between 100 and 300 nm. Distinctive endothermic peaks were observed for the SeCyst-Pul aggregate solutions based on a differential scanning calorimetric analysis. The tryptophan (Trp) fluorescence intensity of SeCyst benzyl ester-tryptophanyl-Pul (SeCyst-Bz-Trp-Pul) mostly decreased in comparison to those of the Trp-Pul (its precursor) and free Trp, which indicates that the Trp residues come close to each other during the aggregation of the conjugates. Formation of SeCyst-Pul aggregates could be induced by the hydrophobic interactions between the SeCyst esters and the amino acid residues on Pul. The GPx-like activity of SeCyst-Bz-Trp-Pul aggregates for the reduction of H2O2 was enhanced nearly 20-fold higher than that of free SeCyst. The double-reciprocal plots of the SeCyst-Bz-Trp-Pul aggregate-catalyzed reduction yielded parallel lines by varying the substrate concentrations, indicating a "ping-pong" mechanism that is similar to those of the natural GPxs. The enhanced GPx activity of the SeCyst-Bz-Trp-Pul aggregate was also supported by higher kinetic parameters, k(cat)/K(m) (GSH) and k(cat)/K(m) H2O2. Overall, the enhanced activity of the SeCyst-Bz-Trp-Pul aggregate would be attributed to a hydrophobic environment that was formed at the vicinity of the SeCyst.
authors.affiliation: Graduate School of Biomedical Sciences, Nagasaki University, 1-14, Bunkyo-machi, Nagasaki 852-8521, Japan. haratake@nagasaki-u.ac.jp
authors.forename: Mamoru
authors.initials: M
authors.lastname: Haratake
authors.forename: Shinya
authors.initials: S
authors.lastname: Matsumoto
authors.forename: Masahiro
authors.initials: M
authors.lastname: Ono
authors.forename: Morio
authors.initials: M
authors.lastname: Nakayama
mesh_terms: D040761:Biomimetic Materials / Q000138:chemical synthesis*; D002152:Calorimetry, Differential Scanning; D002384:Catalysis; D003553:Cystine / Q000031:analogs & derivatives* / Q000737:chemistry; D005936:Glucans / Q000737:chemistry*; D005979:Glutathione Peroxidase / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D057927:Hydrophobic and Hydrophilic Interactions; D007700:Kinetics; D053758:Nanoparticles / Q000737:chemistry*; D016566:Organoselenium Compounds / Q000737:chemistry*; D012542:Scattering, Radiation
chemical_list: D005936:Glucans; D016566:Organoselenium Compounds; C009226:selenocystine; D003553:Cystine; C009109:pullulan; D005979:Glutathione Peroxidase