Polymerization of 4-Hydroxyphenyl .ALPHA.-Glucoside and 4-Hydroxyphenyl .BETA.-Glucoside Catalyzed by Horseradish Peroxidase
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Polymerization processes of 4´-hydroxyphenyl α-glucoside (α-Arb) and 4´-hydroxyphenyl β-glucoside (arbutin, β-Arb) catalyzed by horseradish peroxidase (HRP) were analyzed in detail. A calculated model based on the coupling of the free radicals formed from the substrates with every degree of polymerization reproduced successfully most of the experimental results: An increase of the polymer with a decrease of the monomer and a temporal accumulation of the dimer responding to the addition of H2O2. Reaction controlled at neutral pH improved the polymer yields by preventing partial hydrolysis of the glucose residues. A sequential addition of divided portions of H2O2 also increased the yields considerably compared to the single addition, although the yields with too low enzyme activities could not be restored. The main chain structure of the α-Arb polymer was the same as that of the β-Arb polymer which had linkages at the 3´- and 5´-positions of hydroquinone moieties. The polymers showed molecular weight distribution at 1-25 kDa in gel permeation chromatography, when maltooligosaccharides and pullulan were used as standards. Mass spectrometric analysis of deglycosylated polymers suggested that the α-Arb polymer contained smaller components more than the β-Arb polymer. Peroxidases from horseradish, soybean and Arthromyces polymerized β-Arb faster than α-Arb. HRP polymerized the two glucosides faster than the other two peroxidases. Oxidation potentials were determined to be 821 and 835 mV for α-Arb and β-Arb, respectively, by cyclic voltammetry, suggesting almost the same electrochemical reactivity. A higher reactivity of β-Arb in the enzymatic polymerization was thus attributed not to electrochemical reactivity of the substrates, but to stereoselectivity of the enzymes.
- 日本応用糖質科学会の論文
日本応用糖質科学会 | 論文
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