Km and Vmax Beef Liver Catalaese
Bioimpacts. 2017; 7(3): 147–153.
Investigation of the binding machinery and inhibition of bovine liver catalase by quercetin: Multi-spectroscopic and computational study
Samaneh Rashtbari
iDepartment of Biology, Faculty of Natural Sciences, Academy of Tabriz, Tabriz, Iran
Gholamreza Dehghan
1Department of Biological science, Faculty of Natural Sciences, Academy of Tabriz, Tabriz, Iran
Reza Yekta
1Department of Biology, Faculty of Natural Sciences, University of Tabriz, Tabriz, Iran
Abolghasem Jouyban
2Pharmaceutical Analysis Research Center and Kinesthesia of Pharmacy, Tabriz Academy of Medical Sciences, Tabriz, Islamic republic of iran
Received 2017 Jun xx; Revised 2017 Jul i; Accepted 2017 Jul 8.
Abstruse
Introduction: The report on the side effects of diverse drugs and compounds on enzymes is a main upshot for monitoring the conformational and functional changes of them. Quercetin (3,5,7,3ʹ,4ʹ-pentahydroxyflavone, QUE), a polyphenolic flavonoid, widely found in fruits, vegetables and it is used as an ingredient in foods and beverages. The interaction of bovine liver catalase (BLC) with QUE has been studied in this enquiry by using different spectroscopic methods.
Methods: In this work, the interaction of QUE with BLC was investigated using different spectroscopic methods including ultraviolet-visible (UV-vis) absorption, circular dichroism (CD) and fluorescence spectroscopy and molecular docking studies.
Results: Fluorescence information at dissimilar temperatures, synchronous fluorescence and CD studies revealed conformational changes in the BLC structure in the presence of unlike concentration of QUE. Too, the fluorescence quenching data showed that QUE tin can grade a non-fluorescent complex with BLC and quench its intrinsic emission past a static procedure. The bounden constant (Ka) for the interaction was 104, and the number of binding site was obtained ~1. The ∆H, ∆S and ∆G changes were obtained, indicating that hydrophobic interactions play a main role in the circuitous formation. In vitro kinetic studies revealed that QUE tin can inhibit BLC activity through non-competitive manner. Molecular docking study results were in good agreement with experimental information, confirming only one binding site on BLC for QUE at a cavity amongst the wrapping domain, threating arm and β-barrel.
Determination: Inhibition of BLC activity upon interaction with QUE demonstrated that in addition to their beneficial effects, they should not exist overlooked for their side furnishings.
Keywords: Bovine liver catalase, Flavonoid, Molecular docking, Not-competitive inhibition, Quercetin, Static quenching
Introduction
Catalase (HiiO2:H2O2 oxidoreductase, EC i.11.1.6) is a ubiquitous enzyme. Information technology protects organelles and tissues against hydrogen peroxide (H2O2) and reactive oxygen species (ROS) toxicity. Catalase deficiency and oxidative stress accept been detected in association with various disorders including hypertension, vitiligo, diabetes mellitus, Alzheimer disease, acatalasemia and cancer.one,2 Catalase converts HtwoOii to molecular oxygen and water in 2 steps. In the offset step (equation 1) the heme iron is oxidized past using H2Oii to form compound I (Cpd I). In the side by side footstep (equation 2) Cpd I is reduced by using the 2d molecule of H2Otwo.3
E(p o r −F due east I I I ) +H 2 o ii®CompoundI(p o r −+ −F east I V =o) +H 2 o ii
(one)
(2)
Bovine liver catalase (BLC) i, a tetrameric enzyme, composed of four identical subunits with 1 heme per subunit. Each subunit consists of 4 domains: an eight-stranded β-butt, α-helical domain, Due north-terminal threading arm and wrapping loop which connects the N-terminal threading arm to β-barrel. Also, catalase binds NADPH at the surface of the molecule at a crevice between the helical domain and β-barrel. Studies revealed that NADPH plays many functions. It can subtract the formation of compound 2, increase its removal and inhibits the enzyme at low concentration of H2O2.4,5
Flavonoids are polyphenolic compounds that belong to a class of water-soluble plant pigments. They mainly present in vegetables, fruits, tea, wine, and fruit drinks and happen to be a component of the man diet. They show lots of biological and pharmacological properties including anti-oxidant, anti-cancer, anti-inflammatory and anti-obesity effects.vi-10 Flavonoids are divided into vi categories including flavonols, flavones, flavanones, isoflavones, flavanols and anthocyanidins.xi,12
Quercetin (3,five,7,3ʹ,4ʹ-pentahydroxyflavone, QUE) (Fig. 1) belongs to the flavonol subclass of flavonoids. QUE nowadays in most plants and fruits. Information technology exists in the human nutrition as high as 25-40 mg/d.13 QUE is an anti-oxidant agent due to its ability to metal chelation and scavenging oxygen complimentary radicals. Complexation of metallic cations by QUE has been reported for a big number of metals such as Atomic number 26(II), Fe(III), Zn(Two), Co(Two), Tb(3), Tb(2) and Sn(II).14,xv
Chemical construction of quercetin.
It has been reported that flavonoids inhibit some enzymes including xanthine oxidase, cytochromes P450, cyclooxygenases and lipoxygenases. Also, several in vivo and in vitro studies have shown that flavonoids can decrease catalase expression and activity. Krych and Gebicka have reported that various flavonoids from flavonols, flavones and flavanols (catechins) subclasses, can efficiently react with catalase and inhibit its activity.16 So in this report, the possible effects of QUE, every bit a polyphenol natural products from the flavonoid grouping, was investigated on the conformation and function of BLC by several methods. Since catalase has high activity in the liver which is one of the largest organs in the trunk with diverse metabolic functions, in which toxic substances are taken up and converted into harmless substances. Therefore, the written report of the side furnishings of diverse compounds and drugs on catalase has been fastened the attention of many researchers. In this work, we investigated the effects of QUE, equally a dietary flavonoid, on the conformation and part of BLC.
Materials and Methods
Materials
BLC (molecular weight 250 KD), quercetin.2H2O and dimethylsulfoxide (DMSO) were purchased from Sigma- Aldrich (St. Louis, MO, USA). Disodium hydrogen phosphate (Na2HPOfour), sodium dihydrogen phosphate (NaH2PO4) and Hydrogen peroxide (HiiO2) xxx% were purchased from Merck Co. (Darmstadt, Federal republic of germany). The QUE stock solution (16.5 mM) was prepared past dissolving in DMSO and was added sufficient distilled h2o to bring the solution to the desired volume. The concentration of the H2O2 stock solution was computed spectrophotometrically, taking the extinction coefficient of 40 One thousand−1 cm−1.16
Methods
Kinetics studies of BLC
The activity of BLC was determined using a UV spectrophotometer (T60, PG Instruments LTD., Leicestershire, Britain) by detecting the subtract in H2O2 maximum absorbance at 240 nm (A240) in sodium phosphate buffer (pH= seven, 50 mM), due to its break down by the enzyme. To investigate the effects of QUE on the activeness of BLC, its 3 nM solution was incubated with different concentrations of QUE (5.5, xi, 16.5, 22 and 27.five μM), in a full volume of 3 mL. After, a fixed concentration of H2O2 (70 mM) was added to the solutions and the absorbance of them was recorded at 240 nm every 2 seconds for one minute.
Spectroscopic investigations
BLC absorption spectra were recorded in the range of 200-500 nm, using ane cm quartz cell. The fluorescence spectra were recorded using a FP-750 Jasco spectrofluorometer (Kyoto, Nippon) at two temperatures (25°C and 37°C) with the excitation wavelength (λex) of 280 nm and the fluorescence emission wavelength (λem) range of 300-500 nm. The synchronous fluorescence spectra of BLC with and without QUE were scanned using Δλ=15 nm (λem=240-400) for tyrosine (Tyr) and Δλ=sixty nm (λem=300-500) for tryptophan (Trp). The scan speed was fixed at thousand nm.min-1.
CD spectra of BLC were recorded on a J-810 spectropolarimeter (Jasco, Tokyo, Japan) in the presence and absence of QUE at room temperature in 0.1 cm cell in 50 mM sodium phosphate buffer. The percentage of secondary structure elements of BLC upon interaction with diverse concentrations of QUE, were estimated by the CDNN software.
Molecular docking report
Molecular docking was carried out to obtain the best binding site of QUE on BLC using the Car Dock software (version 4.ii).17 BLC's crystal construction (PDB ID: 1TGU) was taken from the Poly peptide Data Banking concern. QUE molecular structure was drawn by Hyperchem viii.0.6 and its energy minimized conformation was conducted using Gaussian 03 programs. The Lamarckian genetic algorithm (LGA) search method was used for searching the best binding site of QUE to the BLC. The modes of interaction between BLC and QUE was investigated using Bubble 1.10.1 program.eighteen
Results and Discussion
Kinetics studies
Assay of BLC activity
Catalase breakdowns the H2Oii to HiiO and O2. The rate of decomposition of HtwoO2 by BLC, which leads to decrease in H2O2 absorption at 240 nm, was considered as the enzyme activity. For this purpose, the additional concentrations of H2O2 (10-90 mM) in the presence of the fixed concentration of BLC (three nM) was used to decide the BLC action. The results indicated that with raising HtwoOtwo concentration, BLC action increases (from 10 to 70 mM), after that with more than concentrated solutions of HiiO2 (> 70 mM), a pregnant reduction in BLC action was detected, due to suicide inactivation process.19 Lineweaver-Burk plot and equation 3 were applied to determine the accurate kinetic parameters.
The K 1000 (Michaelis Constant) and 5 max (Maximal Velocity) values were obtained to be 39 mM and ii.28 mM.S-1, respectively. Also, the equation (4) was used to estimate the catalytic constant (1000 cat) value, which was obtained as 7.6 × 105 s-ane.
where [Et] is full enzyme concentration.
In order to investigate the effects of QUE on enzyme action, BLC activity assays were performed in the presence of boosted concentrations of QUE (five.5, 11, 16.5, 22 and 27.5 μM) and fixed concentration of H2Otwo (seventy μM). It has been observed that with an increase in QUE concentration, BLC activity markedly reduced. According to Fig. 2A, the IC50 value was calculated equally 16.76 μM. The inhibition kinetics of BLC by QUE was and so analyzed by a Lineweaver-Burk plot (Fig. 2B) which indicated that QUE is a not-competitive inhibitor of BLC. When the slope of each curve from Fig. 2B was re-plotted confronting different concentrations of QUE a Ki of 46.0 μM was obtained (Fig. 2C).
Result of different concentrations of quercetin (0, 5.v, 11, xvi.5, 22 and 27.5 µM) on the catalytic activity of bovine liver catalase in phosphate buffer 50 mM, pH vii, at room temperature. (B) Lineweaver-Burk curve of bovine liver catalase (3 nm) in the absence and presence of unlike concentrations of quercetin: 0 (×), 8.38 (♦), 16.76 (■) and 33.52 (▲) µM in phosphate buffer l mM, pH 7, at room temperature. (C) The secondary linear plot which derived of Lineweaver–Burk plot.
UV-vis spectrometric investigations
UV-vis assimilation spectrometry is a uncomplicated and effective method, which is applied to investigate the structural modify of proteins upon interaction with ligands. The UV-vis spectrum of BLC shows the main absorption band around 280 nm, which mainly comes from aromatic amino acids. As well, BLC possesses another significant height around 405 nm (Soret-band), which is acquired past the π→π* transition of electrons in the heme group.20,21 UV-vis spectra of BLC (one μM) were measured in different concentrations of QUE (viii.38, sixteen.76 and 33.52 µM). The results indicated that with increasing concentration of QUE both of the absorption peaks (280 and 405 nm) increase, but more investigations showed that QUE has its own absorption in the studied wavelengths (280 and 405 nm), so the absorption values of QUE at dissimilar concentrations were subtracted from the absorption values of BLC-QUE, showing that the interaction between BLC and QUE result in a petty hyperchromic event around 280 nm (Fig. 3A) and 405 nm (Fig. 3B). These results indicated that QUE tin form complex with BLC and change its construction slightly.xix
The changes in bovine liver catalase absorption (1 µM) at 280 nm (A) and 405 nm (B) afterwards addition of quercetin in phosphate buffer fifty mM, pH vii, at room temperature.
Fluorescence spectroscopy
Fluorescence spectroscopy is a fast, robust and highly sensitive tool, which is applied to study the structural changes of macromolecules upon interaction with various ligands. The intrinsic fluorescence emission of BLC results from aromatic fluorophores (dominantly Trp and Tyr residues). The intrinsic fluorescence emission of tryptophan is very sensitive to the polarity of the surrounding environment.22 We used fluorescence spectroscopy to investigate the interaction between QUE and BLC. Equally tin be seen from Fig. iv, the fluorescence intensity of BLC decreases in the presence of an boosted concentration of QUE (one, 2, 3, 4, 5 and 6 µM). Results indicated that QUE tin quench the intrinsic fluorescence of BLC and modify the micro-region environment around the fluorophores (excitation wavelength was set at 280 nm).
Upshot of concentration of quercetin on fluorescence intensity of bovine liver catalase before and after add-on of quercetin. λex=280 nm, BLC concentration: (0.seven µM); quercetin concentrations:(a) 0, (b) 1, (c) 2, (d) 3, (due east) 4, (f) five, (yard) half dozen.
Fluorescence quenching mechanisms are classified into 2 types by their dissimilar dependence on temperature: dynamic (collisional quenching) and static (non-fluorescent circuitous formation). In order to estimate the quenching mechanism of BLC in the presence of QUE, Stern-Volmer equation (five) was used:
(5)
where, F and F 0 are the fluorescence intensities of BLC with and without the quencher (QUE), respectively, [QUE] is the concentration of the quencher, K q is the quenching rate constant of the biomolecule, τ0is the fluorescence lifetime without quencher (10-viii southward for BLC) and KSVis the Stern–Volmer quenching constant. The careful examination of the plot of F 0 /F vs. [QUE] (Fig. 5) revealed that the G SV values decrease with an increase in temperature, and M q values are much greater than ii×tenten L mol-1 due south-1, which are feature of static quenching machinery.23
Stern-Volmer plot for fluorescence quenching of bovine liver catalase by dissimilar concentrations of quercetin at 298 K (♦) and 310 K (■).
Synchronous fluorescence spectroscopy
Synchronous fluorescence spectroscopy provides of import information most the micro-region effectually the fluorophores. By scanning simultaneously both excitation and emission wavelengths, maintaining a constant wavelength interval (∆λ) between them (∆λ=15 nm for Tyr and ∆λ=60 nm for Trp).24 The gradual decrease in the fluorescence intensity on the successive additions of QUE is an obvious indication of the circuitous germination between BLC and QUE, but the peak positions of the synchronous fluorescence spectra remain unshifted (Fig. 6A and 6B). Information technology seems that the bounden of QUE to BLC has no obvious effect on the microenvironment effectually the Tyr and Trp residues.25
Synchronous fluorescence emission spectra of bovine liver catalase in the presence of different concentrations of quercetin (0, 1, 2, 3 and 4 µM); (A) ∆λ=fifteen and (B) ∆λ=60 nm, (f) simply quercetin 1 µM, at room temperature.
Circular dichroism spectroscopy study
To gain a better agreement of QUE effects on the secondary construction of BLC, CD spectroscopy was used. Fig. vii shows the CD spectra of BLC in the presence or absence of dissimilar concentrations of QUE in the far-UV spectral region (190-250 nm). The CD spectra of BLC exhibits two negative bands at 208 and 222 nm (characteristic of the α-helical structure of the protein) and a negative ring around 217 nm (related to β-sheets). The CD spectra recorded were analyzed using CDNN software and obtained results were summarized in Tabular array 1. Co-ordinate to Table 1, the content of the α-helical structure in BLC increased from 26.4% to 30.three%, while the content of β-sheet decreased from 21.7% to 19.1%, suggesting the considerable changes in the poly peptide secondary structure. Also, the results signal that QUE can increase the stability of BLC via increasing the α-helical structures and reduction of other secondary elements of protein.26
Change in CD spectra of bovine liver catalase with and without diverse concentrations of quercetin at room temperature.
Tabular array 1
Content of secondary structure elements of bovine liver catalase (BLC) with and without of quercetin at room temperature
| Molar rate of BLC to quercetin | Secondary construction (%) | |||
| α-Helix | β-Sheet | β-Turns | Random coil | |
| 2:0 | 26.4 | 21.7 | 18.1 | 33.8 |
| ii:10 | 29.5 | 20.two | 17 | 33.3 |
| 2:twenty | 30.3 | 19.1 | eighteen.8 | 33.6 |
Thermodynamic analysis and binding style
In order to calculate the number of binding sites (n) and binding constant (G a ), the following equation was used:
(7)
According to a plot of vs. (Fig. 8), the 1000 a and "n" values were obtained and the results have been summarized in Table 2. The results indicated that in that location is but 1 binding site on BLC for QUE (n ~ 1) and the K a value increased with the increasing temperature, suggesting that the stability of circuitous increase with the ascension temperature. The K a value was about 10iv, indicating that there is a stiff interaction between QUE and BLC.27
The linear plot of vs. log [quercetin], according to equation 7, for fluorescence quenching of bovine liver catalase in the presence of quercetin at 298K (♦) and 310K (■).
Table 2
Bounden parameters of bovine liver catalase (BLC)- quercetin complex at 25ºC and 37ºC
| Temperature (°C) | north | Yard SV (×10 v M -one ) | K q (×x xiii M -1 s -1 ) | K a (×10 4 1000 -one ) | ΔG (kJmol -1 ) | ΔH(kJmol -one ) | ΔS (JK -1 mol -one ) |
| 25 | 0.97 | two.xviii | two.18 | 16.04 | -29.69 | +105.8 | +454.66 |
| 37 | ane.13 | ane.69 | i.69 | 83.98 | -35.15 |
There are diverse kinds of acting forces between a ligand and a macromolecule, which are classified into four groups based on the sign and the magnitude of the calculated parameters: 1) ∆H˂ 0 and ∆S > 0 (electrostatic forces play the principal role), two) ∆H ˃ 0 and ∆S ˃ 0 (hydrophobic interactions are of import), iii) ∆H ˂ 0 and four) ∆S ˂ 0 (van der Waals forces and hydrogen bonding are ascendant).28 Table 2 summarized the numerical values of ∆H, ∆S and ∆One thousand calculated according to equations 8-10.
The positive values of enthalpy changes (∆H) and the entropy changes (∆South) signal that the hydrophobic interactions are involved in the circuitous formation between BLC and QUE. As well, the ΔG values are negative, indicating that interaction of QUE with BLC is a spontaneous procedure.23,27
Molecular docking results
To predict the best bounden sites of QUE on BLC molecular docking studies were performed. Fig. ix(A and B) shows that the best binding site of QUE on BLC is located abroad from heme group, at a cavity amid the wrapping domain, threating arm and β-barrel, confirmation that the QUE is a not-competitive inhibitor. Fig. 9C shows the involving amino-acid residues in the interaction of BLC and QUE (Pro 367, Gln 386, Gln 397, Met 394, Asn 368, Tyr 369, Gln 371, Leu 370, Cys 376, Pro 377 and Val 382). Information technology is articulate that QUE interacts with BLC through hydrophobic interaction and hydrogen bonding, but hydrophobic interactions are dominant. The molecular docking results illustrated that there is one bounden site for QUE on BLC. The value of lowest binding costless energy was calculated as -seven.21 kcal mol-1.
Molecular docking results for complex of bovine liver catalase with quercetin (A) The carton form of 1 subunit of bovine liver catalase and (B) in hydrophobic surface model. (C) bovine liver catalase and quercetin amino acrid residues in the binding site.
Determination
Flavonoids are polyphenolic secondary metabolites in plants and mainly present in vegetables and fruits and they used as dietary supplements. Previous studies take been reported that flavonoids tin inhibit catalase action, and so in this piece of work, we investigated the interaction between QUE, i of the all-time-known flavonoids, and BLC. In vitro studies indicated that QUE (27.five µM) has an inhibitory outcome on catalase activeness. The machinery of inhibition was a not-competitive process. QUE binds to BLC through i bounden site. The CD Spectroscopic results revealed that the conformational changes in BLC structure were acquired by QUE. Fluorescence spectroscopy information indicated that QUE can quench fluorescence intensity of BLC past a static mechanism, only information technology cannot change the microenvironment of Tyr and Trp residues. The all-time interaction way betwixt QUE and BLC adamant using molecular docking study. So, this report provides some evidence for evaluating the toxicity furnishings of QUE to catalase. Co-ordinate to the literature, the dietary intake of all flavonoids is about 200–350 mg/d, of which QUE accounts is approximately x mg/d. As QUE is present in vegetables and fruits, high consumption of such foods can increment intake to over 200 mg/d. So, according to our data excessive intake of the antioxidants such as QUE could be associated with some side furnishings.
Competing interests
The authors declare no competing interests.
Ethical approval
At that place is none to be declared.
Research Highlights
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