RESUMO
Glucan branching enzymes (GBEs, EC 2.4.1.18) catalyze the formation of α-1,6-linked branch in starch, which is important for the starch modification with prospective properties. In this study, the aqGBE gene encoding an efficient glucan branching enzyme was cloned from Aquabacterium sp. strain A7-Y and successfully expressed in Escherichia coli BL21 (DE3). The specific activity of the purified recombinant enzyme rAqGBE was 2850 U/mg with potato starch as the optimal substrate, and the Km and Vmax values of rAqGBE were 1.18 mg/mL and 588.2 µmol/min/mg, respectively. Enzymological characterization showed that rAqGBE exhibits its optimal activity under the condition of 40 °C and pH 7.0, respectively, which is independent of calcium ions. Otherwise, rAqGBE-treated potato starch showed different chain length distribution compared with control, the numbers of short chains (degree of polymerization, DP < 7) and long chains (DP > 25) increased from 4.5% to 9.6% and 6.1%-15.7% after enzymatic treatment, respectively. In starch anti-ageing assay, with minimum usage of 0.8 mg rAqGBE per g starch, the rAqGBE-treated potato starch exhibited reduced retrogradation properties. Our results indicate that the branching enzyme AqGBE may therefore be a promising tool for the enzymatic modification of starch.
Assuntos
Enzima Ramificadora de 1,4-alfa-Glucana , Proteínas de Bactérias , Burkholderiales/genética , Amido/química , Enzima Ramificadora de 1,4-alfa-Glucana/biossíntese , Enzima Ramificadora de 1,4-alfa-Glucana/química , Enzima Ramificadora de 1,4-alfa-Glucana/genética , Enzima Ramificadora de 1,4-alfa-Glucana/isolamento & purificação , Proteínas de Bactérias/biossíntese , Proteínas de Bactérias/química , Proteínas de Bactérias/genética , Proteínas de Bactérias/isolamento & purificação , Burkholderiales/enzimologia , Escherichia coli/genética , Escherichia coli/metabolismo , Proteínas Recombinantes/biossíntese , Proteínas Recombinantes/química , Proteínas Recombinantes/genética , Proteínas Recombinantes/isolamento & purificaçãoRESUMO
PbMoO4 and PbWO4 are prepared by the simple precipitation method in this work, they show the photocatalytic activities for the degradation of methyl orange in water under the UV light illumination. In the above photocatalytic degradation processes, methyl orange concentration decreases quickly, the total organic carbon (TOC) decreases slowly; inorganic ions (SO4(2-), NO3(-), NO2(-), NH4(+)) can be formed and measured by the ion chromatograph; the pH value in the systems decreases gradually; a small quantity of HOË(-)·can be generated and measured by the terephthalic acid (TA) indirectly. In order to estimate the roles of active species during the above photocatalytic degradation processes, isopropanol, (NH4)2C2O4, and 1,4-benzoquinone as the scavengers for HOË, h(+), O2Ë(-) are introduced into the systems, respectively. Isopropanol and (NH4)2C2O4 are effective scavengers for active species HOË and h(+) respectively, but 1,4-benzoquinone is not a satisfactory scavenger in all cases to capture O2Ë(-), at least in this work. At last, PbMoO4 and PbWO4 are characterized by nitrogen sorption, DRS, SEM, TEM and XRD.
