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1.
BACKGROUND: γ‐Aminobutyric acid (GABA) is an important bioactive regulator, and its biosynthesis is primarily through the α‐decarboxylation of glutamate by glutamate decarboxylase (GAD). In plants, it was verified that the production of GABA is regulated, in part, via Ca2+/calmodulin (CaM). Our preliminary studies showed that rice bran GAD is probably also a Ca2+/CaM dependent enzyme; hence, in the current investigation, we purified calmodulin from rice bran, and studied the effect of the Ca2+/calmodulin complex on the activity of rice bran GAD in vitro. RESULTS: CaM was purified to homogeneity from the rice bran by a combined protocol involving TCA precipitation, heat treatment, and hydrophobic interaction chromatography, with the purification fold and recovery of 851.7 and 55.6%, respectively. This protein had similar amino acid composition as the CaMs from other higher plants. The rice bran GAD was found to be quite sensitive to the Ca2+/CaM complex at pH 7.0, and addition of exogenous EGTA or TFP efficiently inhibited the stimulatory effect of Ca2+/CaM complex. At a separate concentration of Ca2+ and CaM of 200 µmol L?1 and 150 nmol L?1, the rice bran GAD was significantly enhanced 3‐fold. Moreover, upon binding Ca2+, CaM underwent a conformational change that facilitated a more obvious emergency of phenylalanine and tyrosine residues. CONCLUSION: This investigation provided preliminary information for the development of a GABA‐based, cost‐effective rice bran GAD‐related functional food. Copyright © 2010 Society of Chemical Industry  相似文献   

2.
Background: γ‐Aminobutyric acid (GABA) is a non‐protein amino acid with bioactive functions for human health. Diamine oxidase (DAO, EC 1.4.3.6) is one of the key enzymes for GABA formation. In the present study, this enzyme was purified from 5 day germinated fava bean and its properties were investigated in vitro. Results: The molecular mass of the enzyme estimated by Sephadex G‐100 gel filtration was 121 kDa. Sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS‐PAGE) displayed a single band at a molecular mass of 52 kDa. The enzyme had optimal activity at 40 °C and retained its activity after being incubated at 30 °C for 30 min. It showed higher activity at pH 6.5 than at other pH values. The enzyme was significantly inhibited by Mg2+, Cu2+, Fe3+, aminoguanidine, ethylene glycol tetraacetic acid (EGTA), ethylene diamine tetraacetic acid disodium salt (EDTA‐Na2), L ‐cysteine and β‐mercaptoethanol. The Km value of DAO was 0.23 mmol L?1 for putrescine and 0.96 mmol L?1 for spermidine. However, the enzyme did not degrade spermine. Conclusion: DAO from germinated fava bean was purified. The optimal reaction temperature and pH of the enzyme were mild. The enzyme had higher affinity to putrescine than to spermidine and spermine. Copyright © 2011 Society of Chemical Industry  相似文献   

3.
BACKGROUND: In Tunisia, sardinelle (Sardinella aurita) catches totalled about 13 300 t in 2002. During processing, solid wastes including heads and viscera are generated, representing about 30% of the original raw material. Viscera, one of the most important by‐products of the fishing industry, are recognised as a potential source of digestive enzymes, especially proteases with high activity over a wide range of pH and temperature conditions. This paper describes the purification procedure and some biochemical characterisation of trypsin from S. aurita viscera. RESULTS: Trypsin from the viscera of sardinelle (S. aurita) was purified by fractionation with ammonium sulphate, Sephadex G‐75 gel filtration, Sepharose mono Q anion exchange chromatography, ultrafiltration and a second Sephadex G‐75 gel filtration, resulting in a 5.42‐fold increase in specific activity and 6.1% recovery. The molecular weight of the purified enzyme was estimated to be 24 kDa using size exclusion chromatography and sodium dodecyl sulfate polyacrylamide gel electrophoresis. The purified enzyme showed esterase‐specific activity on N‐α‐benzoyl‐L ‐arginine ethyl ester (BAEE) that was four times greater than its amidase‐specific activity on N‐α‐benzoyl‐DL ‐arginine‐p‐nitroanilide (BAPNA). The optimal pH and temperature for enzyme activity were pH 8 and 55 °C respectively using BAEE as a substrate. The trypsin kinetic constants Km and kcat on BAPNA were 1.67 mmol L?1 and 3.87 s?1 respectively, while the catalytic efficiency kcat/Km was 2.31 s?1 L mmol?1. CONCLUSION: Trypsin was purified from sardinelle (S. aurita) viscera. Biochemical characterisation of S. aurita trypsin showed that this enzyme can be used as a possible biotechnological tool in the fish‐processing and food industries. Copyright © 2008 Society of Chemical Industry  相似文献   

4.
An aminopeptidase (AP) was partially purified from jumbo squid (Dosidicus gigas) hepatopancreas with 154.24‐fold and yield of 6.15%. The purification procedure consisted of ammonium sulphate fractionation and DEAE‐Sephacel chromatography. The enzyme was approximately 48–53 kDa as estimated by SDS‐PAGE. With l ‐leu‐p‐NA, it had optimum activity at pH 8.0 and 30 °C. The Km and Vmax/Km values of the enzymes for l ‐leu‐p‐NA were 0.326 mm and 2787 at 37 °C, respectively. Activation energy (Ea) of the enzyme was 53.50 kJ M?1.The AP showed activity against seven synthetic substrates: l ‐proline>l ‐methionine>Ac. l ‐γ‐glutamic>l ‐glycine>l ‐leucine>l ‐alanine>l ‐lysine‐p‐NA. The enzyme was strongly inhibited by Bestatin, partially inhibited by a metal‐chelating agent and by PCMB, a cystein protease inhibitor. Zn2+ and (or) Ca2+ seemed to be its metal cofactor(s). Incubation of casein with the partially purified AP resulted in a degree of hydrolysis of 6%.  相似文献   

5.
The extracellular α‐l ‐rhamnosidase has been purified by growing a new fungal strain Aspergillus awamori MTCC‐2879 in the liquid culture growth medium containing orange peel. The purification procedure involved ultrafiltration using PM‐10 membrane and anion‐exchange chromatography on diethyl amino ethyl cellulose. The purified enzyme gave single protein band in SDS‐PAGE analysis corresponding to molecular mass 75.0 kDa. The native PAGE analysis of the purified enzyme also gave a single protein band, confirming the purity of the enzyme. The Km and Vmax values of the enzyme for p‐nitrophenyl‐α‐l ‐rhamnopyranoside were 0.62 mm and 27.06 μmole min?1 mg?1, respectively, yielding kcat and kcat/km values 39.90 s?1 and 54.70 mm ?1 s?1, respectively. The enzyme had an optimum pH of 7.0 and optimum temperature of 60 °C. The activation energy for the thermal denaturation of the enzyme was 35.65 kJ?1 mol?1 K?1. The purified enzyme can be used for specifically cleaving terminal α‐l ‐rhamnose from the natural glycosides, thereby contributing to the preparation of pharmaceutically important compounds like prunin and l ‐rhamnose.  相似文献   

6.
BACKGROUND: Proteases have become an essential part of the modern food and feed industry, being incorporated in a large and diversified range of products for human and animal consumption. The objective of this study was to purify and characterise a protease from wheat germ. RESULTS: After purification a single protease of molecular weight 61–63 kDa (determined by sodium dodecyl sulfate polyacrylamide gel electrophoresis) was obtained. The purified protease had optimal activity at 50 °C and maintained its activity completely after incubation at 30 °C for 30 min, while over 47% of the activity was lost after incubation at 80 °C for 30 min. The purified protease had optimal activity and maintained maximum stability at pH 5.5, while the activity decreased after incubation for 30 min at other pH values. The protease was inhibited by Mg2+, Mn2+, Ba2+ and iodacetic acid and stimulated by Li+, Ca2+, Cu2+, β‐mercaptoethanol and dithiothreitol, while Zn2+, L ‐cysteine and glutathione had no significant effect on its activity. At pH 5.5 the enzyme had a Km of 0.562 mg mL?1 with casein as substrate and showed higher affinity to casein than to bovine serum albumin, ovalbumin and gelatin. CONCLUSION: The purified enzyme from wheat germ was identified as a cysteine protease. Copyright © 2011 Society of Chemical Industry  相似文献   

7.
An α‐l ‐rhamnosidase secreted by Penicillium citrinum MTCC‐8897 has been purified to homogeneity from the culture filtrate of the fungal strain using ammonium sulphate precipitation and cation‐exchange chromatography on carboxymethyl cellulose. The sodium dodecyl sulphate/polyacrylamide gel electrophoresis analysis of the purified enzyme gave a single protein band corresponding to the molecular mass 51.0 kDa. The native polyacrylamide gel electrophoresis also gave a single protein band confirming the enzyme purity. The Km and Vmax values of the enzyme for p‐nitrophenyl α‐l ‐rhamnopyranoside were 0.36 mm and 22.54 μmole min?1 mg?1, respectively, and kcat value was 17.1 s?1 giving kcat/Km value of 4.75 × 104 m ?1 s?1. The pH and temperature optima of the enzyme were 7.0 and 60 °C, respectively. The purified enzyme liberated l ‐rhamnose from naringin, rutin, hesperidin and wine, indicating that it has biotechnological application potential for the preparation of l ‐rhamnose and other pharmaceutically important compounds from natural glycosides containing terminal α‐l ‐rhamnose and also in the enhancement of wine aroma.  相似文献   

8.
Quince fruit polyphenol oxidase (PPO) was partially purified using a combination of phase partitioning in Triton X‐114 and PEG 8000/phosphate with a final ammonium sulfate fractionation between 30% and 75%, to avoid the deep browning of the enzyme due to the high amount of oxidizing substances present in the quince pulp. The clean and stable enzyme was partially purified in a latent form and could be optimally activated by the presence of 0.5 g dm?3 sodium dodecyl sulfate (SDS) with an optimum pH of 5.0. In the absence of SDS, the enzyme showed maximum activity at acid pH. The apparent kinetic parameters of the latent enzyme were determined at pH 5.0, the Vm value being 15 times higher in the presence of SDS than in its absence, whereas the KM was the same in both cases, with a value of 1.2 mmol L?1. The effect of several inhibitors was studied, tropolone being the most active with a Ki value of 4.7 µmol L?1. In addition, the effect of cyclodextrins was studied, and the complexation constant (Kc) between 4‐tert‐butylcatechol and cyclodextrins was calculated using an enzymatic method. The value obtained for Kc was 15 310 mol L?1. Copyright © 2006 Society of Chemical Industry  相似文献   

9.
米糠谷氨酸脱羧酶的酶学性质研究   总被引:1,自引:0,他引:1  
研究了米糠谷氨酸脱羧酶(GAD)的酶学性质。结果表明:米糠GAD的最适温度为40℃,最适pH5.6,米糠GAD耐热性较差,60℃下保温0.5 h后,酶活下降至65%,保温1 h,酶活下降至48%,而70℃时酶就完全失活,而此酶在pH5.5~9都可以保持84%以上的酶活力。米糠GAD对底物和辅酶PLP的Km分别为0.028 45 mol/L和1.13μmol/L。KI、Ag~(2+)、SDS、乙酸对米糠GAD的活力有较大的抑制作用,而Ca~(2+)对米糠GAD的活性有较强的激活作用,提高了底物与米糠GAD的亲和力。  相似文献   

10.
Arabinoxylans (AXs) from wheat malts potentially affect beer quality and production. β‐ d ‐Xylosidase is a key enzyme that degrades the main chains of AXs to produce xylose. This study performed a partial characterization of β‐ d ‐xylosidase from wheat malts. The optimal temperature was 70 °C and the enzyme exhibited excellent thermostability, that is, residual activities were 92.6% at 60 °C for 1 h. The enzyme was stable over a pH range of 3.0–6.0 and showed optimum activity at pH 3.5 and 4.5. Kinetic parameters Km and Vmax of wheat malt β‐ d ‐xylosidase against p‐nitrophenyl‐xyloside were 1.74 mmol L−1 and 0.76 m m min−1, respectively. The enzyme activity was severely inhibited by Cu2+, moderately inhibited by Mn2+, Mg2+, Al3+, Ca2+, Ba2+ and Na+ and mildly inhibited by Fe3+ and Fe2+. The partial enzymatic characterization achieved in this study can be used as a theoretical basis for purifying β‐ d ‐xylosidase from wheat malts. Copyright © 2015 The Institute of Brewing & Distilling  相似文献   

11.
12.
An extracellular α‐l ‐rhamnosidase from Penicillium citrinum MTCC‐3565 has purified to homogeneity from its culture filtrate using ethanol precipitation and cation‐exchange chromatography on carboxymethyl cellulose. The purified enzyme gave a single protein band corresponding to molecular mass of 45.0 kDa in SDS‐PAGE analysis showing the purity of the enzyme preparation. The native PAGE analysis showed the monomeric nature of the purified enzyme. Using p‐nitrophenyl α‐l ‐rhamnopyranoside as substrate, Km and Vmax values of the enzyme were 0.30 mm and 27.0 μm min mg?1, respectively. The kcat value was 20.1 s giving kcat/Km value of 67.0 mm s?1 for the same substrate. The pH and temperature optima of the enzyme were 8.5 and 50 °C, respectively. The activation energy for the thermal denaturation of the enzyme was 29.9 KJ mol?1. The α‐l ‐rhamnosidase was able to hydrolyse naringin, rutin and hesperidin and liberated l ‐rhamnose, indicating that the purified enzyme can be used for the preparation of α‐l ‐rhamnose and pharmaceutically important compounds by derhamnosylation of natural glycosides containing terminal α‐l ‐rhamnose. The α‐l ‐rhamnosidase was active at the level of ethanol concentration present in wine, indicating that it can be used for improving wine aroma.  相似文献   

13.
Polyphenol oxidase (PPO), the enzyme responsible for the postharvest spoilage of fruits, was extracted and purified from Uapaca kirkiana peel and pulp by ammonium sulfate precipitation and dialysis. Further purification of peel PPO was carried out by gel filtration chromatography. Optimum pH values were 7 and 8 for peel and pulp PPO, respectively. The optimum temperatures for peel and pulp PPO were 45 and 35 °C, respectively. Inhibition studies of the PPO enzyme were performed using citric acid, sodium azide, sodium metabisulfite and thiourea. The most effective inhibitors were sodium azide and citric acid for both peel and pulp PPO. Vmax and Km values were 13.63 units min?1 and 4.923 mmol L?1, respectively, for peel PPO and 14.03 units min?1 and 5.43 mmol L?1, respectively, for pulp PPO. Three isoenzymes of Uapaca kirkiana PPO were detected by polyacrylamide gel electrophoresis. One of the isoenzymes could be identified as having a molecular weight of 26 625 Da. Copyright © 2005 Society of Chemical Industry  相似文献   

14.
Lysyl oxidase (LOX; E.C.1.4.3.13) was purified from jumbo squid muscle (Dosidicus gigas) with 1900‐fold and yield 1.9%, and characterized for the first time. The purification procedure consisted of fractionation with urea and a combination of size‐exclusion and anion‐exchange chromatography. The enzyme had a molecular weight of 32 kDa, as estimated by SDS‐PAGE. Using a specific LOX substrate (1,5‐diaminopentane), its optimum activity was determined at pH 8.2 and 65 °C. Activation energy (Ea) of the enzyme was 69.94 kJ K?1 mol?1. The enzyme was strongly inhibited by β‐aminopropionitrile fumarate (BAPN), a specific LOX inhibitor. Moreover, purified LOX was able to work at different temperatures (20–90 °C) at pH 8.2. Although further research is needed, the results from this work suggest that based on LOX activity, this enzyme may be of practical use in preventing textural changes in jumbo squid during storage or processing.  相似文献   

15.
BACKGROUND: Oil production from rice bran, an undervalued by‐product of rice milling, produces defatted rice bran (DRB) as a waste material. Although it is considered a less valuable product, DRB still contains useful substances such as phenolic compounds with antioxidant, UV‐B‐protecting and anti‐tumour activities. In this study the phenolic acids in DRB were extracted with subcritical water at temperatures of 125, 150, 175 and 200 °C. RESULTS: Analysis of total phenolics using Folin–Ciocalteu reagent showed about 2–20 g gallic acid equivalent kg?1 bran in the extracts. High‐performance liquid chromatography analysis showed low contents of phenolic acids (about 0.4–2 g kg?1 bran). Ferulic, p‐coumaric, gallic and caffeic acids were the major phenolic acids identified in the extracts. Thermal analysis of the phenolic acids was also done. The thermogravimetric curves showed that p‐coumaric, caffeic and ferulic acids started to decompose at about 170 °C, while gallic acid did not start to decompose until about 200 °C. CONCLUSION: Subcritical water can be used to hydrolyse rice bran and release phenolic compounds, but the high temperatures used in the extraction can also cause the decomposition of phenolic acids. Copyright © 2010 Society of Chemical Industry  相似文献   

16.
β‐galactosidase was isolated from almond (Amygdalus communis) extract by ammonium sulfate precipitation. Almond proteins precipitated by using ammonium sulfate and then dialysed exhibited 5.3‐fold purification of β‐galactosidase, and the yield of enzyme preparation was 96.5%. The partially purified β‐galactosidase exhibited pH and temperature optima at pH 5.5 and 50 °C, respectively. The enzyme was significantly stable against heat, pH, calcium and magnesium ions and D ‐galactose. The almond β‐galactosidase preparation exhibited over 89% activity even after 2 months storage at 4 °C. Hydrolysis of lactose in milk and whey was performed in a stirred batch process by using this enzyme preparation. These observations indicated that the hydrolysis of lactose increased continuously with time. The enzyme could hydrolyse 94% of lactose in buffer solution and whey whereas 90% of lactose hydrolysis was achieved in milk. The main aim of the present study was to prepare lactose‐free milk, which must be free from contamination, and the process should be inexpensive. Copyright © 2007 Society of Chemical Industry  相似文献   

17.
A protease from sorghum malt variety KSV8–11 was purified by a combination of dialysis against 4 M sucrose, ion‐exchange chromatography on Q‐Sepharose (Fast flow), gel filtration chromatography on Sephadex G‐100 and hydrophobic interaction chromatography on Phenyl Sepharose CL‐4B. The enzyme was purified 5‐fold to give a 14.1% yield relative to the total activity in the crude extract and a final specific activity of 1348.9 U mg?1 protein. SDS‐PAGE revealed a single migrating protein band corresponding to a relative molecular mass of 16 KDa. Using casein as substrate, the purified protease had optimal activity at 50°C and maximal temperature stability between 30°C and 40°C but retained over 64% of its original activity after incubation at 60°C for 30 min. The pH optimum was 5.0 with maximum stability at pH 6.0 but 60% of the activity remained after 24 h between pH 5.0 and 8.0. The protease was inhibited by Ag+, Ca2+, Co2+, Fe2+, Mg2+, iodoacetic acid (IAA) and p‐chloromercuribenzoate (p‐CMB), stimulated by Cu2+, Sr2+, phenylmethylsulfonyl‐fluoride (PMSF) and 2‐mercaptoethanol (2‐ME) while Mn2+ and ethylenediaminetetraacetic acid (EDTA) had no effect. The purified enzyme had a Km of 18 mg·mL?1 and a Vmax of 11.1 μmol · mL?1 · min?1 with casein as substrate.  相似文献   

18.
The association of continuous flow injection and spectrophotometry affords a simple, novel and rapid way of monitoring continuously the activity of naturally immobilized enzymes in their natural environment, thus eliminating cumbersome purification. The method was applied to determine the activity of polyphenol oxidase (PPO) enzymes naturally immobilized on coconut (Cocus nucifera, L.) fiber tissues. Maximum enzyme activity occurred at a temperature of 25C and at pH 6.0 using catechol as substrate. Thermal stability was assayed in a temperature range of 20 to 75C. The PPO exhibited excellent thermal stability, with only 50% loss in its activity at 75C after 4.3 min exposure. For catechol apparent Michaelis‐Menten constant (apparent Km), apparent Vmax and the apparent activation energy were 9.1 × 10?3 mol L?1, 0.20 abs min?1 and 10.5 kcal mol?1, respectively. The immobilized PPO showed high activity for o‐diphenols. The reactivity order was caffeic acid > pyrogallol > catechol. Complete inhibition of the enzyme was observed with 1 × 10?3 mol L?1 concentration of cyanide, thiourea, L‐cysteine, ascorbic acid, sodium sulfite, nitrates of cadmium, zinc and mercury, individually. Benzoic acid, 3‐hydroxy‐benzoic acid, 4‐acetamidephenol, sodium azide, resorcinol, L‐cystine and EDTA at equal concentrations inhibited PPO partially.  相似文献   

19.
BACKGROUND: Chemical constituents of the neem tree are extensively explored; the major component present in the tree is azadirachtin. Azadirachtin, a tetranortriterpenoid, is remarkable for its chemical complexity and for its biological activity. This study, for the first time, has provided information on the interaction and inhibition of rice bran lipase (RBL) by azadirachtin. RBL, an esterase, is a versatile enzyme that catalyzes the hydrolysis of ester linkages, primarily in neutral lipids such as triglycerides. RESULTS: The catalytic activity of RBL in the presence of azadirachtin has been investigated. There was a decrease in enzyme activity relative to the control at all concentrations tested. At 1 mmol L?1 concentration of azadirachtin the enzyme loses 84% of its activity. The kinetics of inhibition of RBL by azadirachtin are competitive in nature. From analysis of the kinetic data the inhibition constant Ki is found to be 0.14 mmol. Fluorescence measurements showed a gradual decrease in emission intensity; a red shift in emission maximum may be attributed to perturbation of the aromatic residues. Far‐ultraviolet circular dichroism results showed minor conformational changes. CONCLUSION: The results suggest that azadirachtin specifically inhibits and binds to RBL in bringing about inhibition with minor structural alteration. This inactivation of RBL by azadirachtin can be utilized to prevent oxidation of RBL with an ultimate goal of exploiting the potential of the plant source for producing edible‐grade oil from rice bran using a natural molecule at very low concentration. Copyright © 2009 Society of Chemical Industry  相似文献   

20.
BACKGROUND: The increasing industrial demand for carotenoids has led to growing interest in their bioproduction. The need to reduce production costs has encouraged the use of low‐cost agroindustrial substrates. In this context, this work studied the pretreatment of Mozzarella cheese whey and the use of the pretreated whey as fermentation medium for the bioproduction of carotenoids by Sporidiobolus salmonicolor CBS 2636. RESULTS: Bioproduction was carried out in an orbital shaker using a 10 mL L?1 inoculum, incubation at 25 °C and a stirring rate of 180 rpm for 120 h in a non‐illuminated environment. The carotenoids were recovered using liquid N2 combined with dimethyl sulfoxide for cell rupture and an acetone/methanol mixture (7:3 v/v) for extraction. The maximum concentration of total carotenoids obtained was 590.4 µg L?1 in a medium with 900 g L?1 cheese whey hydrolysate and 4 g L?1 K2HPO4 at 180 rpm, 25 °C and pH 4. CONCLUSION: The use of enzyme‐hydrolysed cheese whey was more effective in carotenoid bioproduction by S. salmonicolor CBS 2636 than the use of acid‐hydrolysed cheese whey. The concentration of total carotenoids obtained with the enzymatic hydrolysate was six times higher than that obtained with the acid hydrolysate. Copyright © 2009 Society of Chemical Industry  相似文献   

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