EUROPEAN FOOD RESEARCH AND TECHNOLOGY
·
2012
·Vol. 234
·期 4
·607-616
·
IF 1.566
Zheng Yongju,Shi Junling,Pan Zhongli
Polyphenol oxidase (PPO) was isolated from Thompson seedless grape ( Vitis vinifera ‘Thompson Seedless’ ), and its biochemical characteristics were studied. The PPO showed activity to catechol and D, L-DOPA, but not towards monophenol l -Tyrosine, diphenols guaiacol and caffeic acid, and triphenols pyrogallic acid and gallic acid. Apparent Michaelis–Menten constant ( K
m ) and maximum velocity of the reaction ( V
max ) values were 45.0 ± 0.05 mM and 500.0 ± 15.3 OD 400 nm /min for catechol, and 34.6 ± 0.03 mM and 384.6 ± 11.7 OD 478 nm /min for D, L-DOPA, respectively. The obtained similar specificity values of V
max / K
m ratio of catechol and D, L-DOPA indicated their similar affinity to Thompson seedless PPO. The most effective inhibitor was l -cysteine, followed in decreasing order by ascorbic acid, sodium metabisulfite, EDTA, NaCl, and citric acid. It was discovered that metal ions of Mg 2+ and Cu 2+ increased, while Zn 2+ and K + reduced the PPO activity. Sugars showed inhibition on the PPO activity, with higher effect by sucrose and lower effect by fructose and glucose. Optimum pH and temperature for grape PPO activity were 6.0 and 25 °C with 10 mM catechol as substrate. The enzyme was heat stable between 10 and 25 °C, but showed significant activity loss at temperatures higher than 40 °C and completely inactivation at 70 °C for 10 min. Thermal inactivation of PPO showed a first-order kinetic with an activation energy ( E
a ) of 146.1 ± 10.8 kJ/mol at pH 6.0.
研究领域:
食品科学
·
生物化学
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产品关联
DOI
高影响因子
CHINESE JOURNAL OF POLYMER SCIENCE
·
2024
·
IF 4.1
Chen Jia-Wen,Xiao Yan,Lang Mei-Dong
Insulin is an essential and versatile protein taking part in the control of blood glucose levels and protein anabolism. However, under prolonged storage or high temperature stress, insulin tends to unfold and aggregate into toxic amyloid fibrils, leading to loss of physiological function. Inspired by natural chaperones, a series of temperature-sensitive polycaprolactone-based micelles were designed to prevent insulin from deactivation. The micelles were fabricated through the self-assembly of amphiphilic copolymers of methoxy poly(ethylene glycol)-poly(4-diethylformamide caprolactone- co -caprolactone) (mPEG 17 -P(DECL- co -CL)), which had a regular spherical morphology with particle sizes of about 100 nm. In addition, the lower critical solution temperature (LCST) of the micelles could be tuned to 9 and 29 °C by changing the ratio of DECL to CL. Benefiting from the temperature-sensitivity of DECL segment, the binding ability of micelles to insulin could be modulated by changing the temperature. Above LCST, micelles effectively inhibited insulin aggregation and protected it from thermal inactivation due to the strong binding ability between the hydrophobic segment DECL and insulin. Below LCST, DECL segment returned to hydrophilic and bound weakly with insulin, leading to the release of insulin and assisting in its recovery of secondary structure. Thus, these temperature-sensitive micelles provided an effective strategy for insulin protection.
研究领域:
生物化学
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材料科学
·
药物递送
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DOI
高影响因子
Foods
·
2021
·Vol. 10
·期 6
·1320
·
IF 4.35
Junping Liu,Jiayan Zhang,Tao Liao,Lei Zhou,Liqiang Zou,Yafei Liu,Li Zhang,Wei Liu
The thermal inactivation kinetics of kudzu (Pueraria lobata) polyphenol oxidase (PPO) were investigated in model and food systems. PPO in kudzu tissue (tPPO) showed a higher thermostability than that of PPO in crude extract (cPPO) and purification fractions (pPPO). The PPO inactivation rate constant (k) increased with an increase in temperature, and tPPO showed the lowestkvalue, followed by that of cPPO and pPPO at the same temperature, indicating that PPO in the food system was more resistant to thermal treatment. Food constituents (pectin, starch, sucrose, and bovine serum albumin) in the food system decreased the activity of PPO but increased the thermostability of PPO, among which pectin exhibited the strongest protective effect against thermal inactivation, and the influence of sucrose was much slighter than that of other macromolecules. Fluorescence emission spectra indicated that pPPO exhibited stronger interactions with pectin than sucrose, and pPPO with pectin showed a more stable conformation under thermal treatment.Keywords:polyphenol oxidase;kudzu;thermostability;thermal inactivation kinetics;food constituents;conformation
研究领域:
食品科学
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酶学
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植物生物化学
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DOI
PubMed
高影响因子
PROTEIN JOURNAL
·
2016
·Vol. 35
·期 4
·318-329
·
IF 1.029
Wu Jing,Yang Xiaolan,Wang Deqiang,Hu Xiaolei,Liao Juan,Rao JingJing,Pu Jun,Zhan Chang-guo,Liao Fei
Prior to the exponential decrease of activity of a uricase from Candida
sp. during storage at 37 °C, there was a plateau period of about 4 days at pH 7.4, 12 days at pH 9.2, and about 22 days in the presence of 30 μM oxonate at pH 7.4 or 9.2, but no degradation of polypeptides and no activity of resolved homodimers. To reveal determinants of the plateau period, a dissociation model involving a serial of conformation intermediates of homotetramer were proposed for kinetic analysis of the thermoinactivation process. In the dissociation model, the roles of interior noncovalent interactions essential for homotetramer integrity were reflected by an equivalent number of the artificial weakest noncovalent interaction; to avoid covariance among parameters, the rate constant for disrupting the artificial weakest noncovalent interaction was fixed at the minimum for physical significance of other parameters; among thermoinactivation curves simulated by numerical integration with different sets of parameters, the one for least-squares fitting to an experimental one gave the solution. Results found that the equivalent number of the artificial weakest noncovalent interaction primarily determined the plateau period; kinetics rather than thermodynamics for homotetramer dissociation determined the thermoinactivation process. These findings facilitated designing thermostable uricase mutants.
研究领域:
生物化学
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酶工程
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DOI
PubMed
高影响因子
APPLIED CATALYSIS B-ENVIRONMENTAL
·
2021
·
IF 19.503
Jin Chen,Xuelong Lv,Wenjian Xu,Xiaolan Li,Jing Chen,Hongpeng Jia
The exploit of simple method to synthesize and recover catalyst is meaningful to widespread application of environmental catalysis. Different from traditional knowledge about deposition of Ag cation by Cl anion, we find that Cl anion coordinates with Ru and Ag cations simultaneously to micro-micelles and results in homogeneously alloying of bimetals. The Ru-Ag alloy exhibits a remarkable activity and stability in propane catalytic oxidation at moderate condition, but is still inactivated by extremely-high temperature and humidity due to metal sintering and oxidation as well as support reconstruction. Fortunately, utilization of Cl coordination to extract and combine bimetals at redox condition is proved as a feasible and simple way to regenerate the thermally-inactivated catalyst. With in-situ characterization, the synergic effect between Ru and Ag on propane oxidation obeying Mars-van-Krevelen mechanism is revealed. Through monolith test, the practice application of Ru-Ag catalyst prepared via Cl-assisted method is thought to be promising.
研究领域:
催化
·
环境化学
·
材料科学
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产品关联
DOI
高影响因子
ENZYME AND MICROBIAL TECHNOLOGY
·
2021
·
IF 3.493
Xinqi Xu,Xiangzhen Deng,Juan Lin,Jie Yang
Arylsulfatase is useful in industrial agar processing by removing sulfate groups. A full-length arylsulfatase gene, designated ArySMA1, was obtained from marine bacteria Serratia sp. SM1. The ArySMA1 gene encoded a novel serine-type arylsulfatase and the enzymatic properties were characterized. The enzyme presented notable capacity of removing sulfate groups from natural algae substrates. Kinetic study suggested that the microscopic thermal inactivation rate of ArySMA1 in free form was smaller than that of the enzyme-substrate complex. The presence of substrate could unexpectedly accelerate ArySMA1 to deactivate at high temperature. Such phenomenon was opposite to many findings that substrate could stabilize enzymes against heat. Molecular dynamics simulation and ANS fluorescent assay indicated the substrate led the hydrophobic regions of the active site more flexible and the sulfate group of the substrate could retard the processivity of ArySMA1 catalysis. This study provides guidance for agar desulfation and down-stream processing industry.
研究领域:
酶学
·
海洋生物技术
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工业生物技术
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产品关联
DOI
PubMed
高影响因子
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