Nanoparticulate Glutathione Peroxidase Mimics Based on Selenocystine−Pullulan Conjugates

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• 作者：Mamoru Haratake ; Shinya Matsumoto ; Masahiro Ono ; Morio Nakayama
• 刊名：Bioconjugate Chemistry
• 出版年：2008
• 出版时间：September 17, 2008
• 年：2008
• 卷：19
• 期：9
• 页码：1831-1839
• 全文大小：206K
• 年卷期：v.19,no.9(September 17, 2008)
• ISSN：1520-4812

文摘

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.