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A Product Inhibition Study on Adenosine Deaminase by Spectroscopy and Calorimetry
Saboury, Ali Akbar,Divsalar, Adeleh,Jafari, Ghasem Ataie,Moosavi-Movahedi, Ali Akbar,Housaindokht, Mohammad Reza,Hakimelahi, Hosain 생화학분자생물학회 2002 Journal of biochemistry and molecular biology Vol.35 No.3
Kinetic and thermodynamic studies have been made on the effect of the inosine product on the activity of adenosine deaminase in a 50 mM sodium phosphate buffer, pH 7.5, at $27^{\circ}C$ using UV spectrophotometry and isothermal titration calorimetry (ITC). A competitive inhibition was observed for inosine as a product of the enzymatic reaction. A graphical-fitting method was used for determination of the binding constant and enthalpy of inhibitor binding by using isothermal titration microcalorimetry data. The dissociation-binding constant is equal to $140\;{\mu}M$ by the microcalorimetry method, which agrees well with the value of $143\;{\mu}M$ for the inhibition constant that was obtained from the spectroscopy method.
Thermodynamic Studies on the Interaction of Copper Ions with Carbonic Anhydrase
A. A. Saboury,S. Mamaghani-Rad,F. Karbassi,N. S. Sarraf 대한화학회 2005 Bulletin of the Korean Chemical Society Vol.26 No.7
The interaction of bovine carbonic anhydrase II with copper ions was studied by isothermal titration microcalorimetry, circular dichroism, UV spectrophotometry and temperature scanning spectrophotometry methods at 27 ûC in Tris buffer solution at pH = 7.5. It was indicated that there are three non-identical different binding sites on carbonic anhydrase for Cu2+. The binding of copper ions is exothermic and can induce some minor changes in the secondary and tertiary structure of the enzyme, which does not unfold it, but can result in a decrease in both activity and stability of the enzyme.
A Product Inhibition Study on Adenosine Deaminase by Spectroscopy and Calorimetry
(Ali Akbar Saboury),(Ghasem Ataie Jafari),(Ali Akbar Moosavi Movahedi),(Mohammad Reza Housaindokht),(Gholam Hosain Hakimelahi),(Adeleh Divsalar) 생화학분자생물학회 2002 BMB Reports Vol.35 No.3
Kinetic and thermodynamic studies have been made on the effect of the inosine product on the activity of adenosine deaminase in a 50 mM sodium phosphate buffer, pH 7.5, at 27oC using UV spectrophotometry and isothermal titration calorimetry (ITC). A competitive inhibition was observed for inosine as a product of the enzymatic reaction. A graphical-fitting method was used for determination of the binding constant and enthalpy of inhibitor binding by using isothermal titration microcalorimetry data. The dissociation-binding constant is equal to 140 μM by the microcalorimetry method, which agrees well with the value of 143 μM for the inhibition constant that was obtained from the spectroscopy method.
A. Hekmat, A. A. Saboury,A. Divsalar,M. Khanmohammadi 대한화학회 2008 Bulletin of the Korean Chemical Society Vol.29 No.8
Results of intrinsic and extrinsic fluorescence studies on choline oxidase revealed that the enzyme at high alkaline pH values has more accessible hydrophobic patches relative to acidic pH. Fluorescence quenching studies with acrylamide confirm these changes. The quenching constants were also determined at different pH(s) by using the Stern-Volmer equation. CD studies showed that at higher pH a transition from α-helix to β- structure was appeared while at lower pH the content of α-helix structure was increased. Furthermore, analysis of the spectral data using chemometric method gave evidence for existence of intermediate components at very high pH(s). Results of thermal denaturation evaluated that the enzyme has the most instability at higher pH(s). Altogether low and high pH values caused significant alteration on secondary and tertiary structures of choline oxidase via inducing of an intermediate.
Gheibi, N.,Saboury, A.A.,Sarreshtehdari, M. Korean Chemical Society 2011 Bulletin of the Korean Chemical Society Vol.32 No.5
Tyrosinase is a widespread enzyme with great promising capabilities. The Lineweaver-Burk plots of the catecholase reactions showed that the kinetics of mushroom tyrosinase (MT), activated by $Co^{2+}$ and $Zn^{2+}$ at different pHs (6, 7, 8 and 9) obeyed the non-essential activation mode. The binding of metal ions to the enzyme increases the maximum velocity of the enzyme due to an increase in the enzyme catalytic constant ($k_{cat}$). From the kinetic analysis, dissociation constants of the activator from the enzyme-metal ion complex ($K_a$) were obtained as $5{\times}10^4M^{-1}$ and $8.33{\times}10^3M^{-1}$ for $Co^{2+}$ and $Zn^{2+}$ at pH 9 and 6 respectively. The structural analysis of MT through circular dichroism (CD) and intensive fluorescence spectra revealed that the conformational stability of the enzyme in these pHs reaches its maximum value in the presence of each of the two metal ions.
Mahshid, Minoo,Saboury, Aboulfazl,Sadr, Seyed Jalil,Fayyaz, Ali,Kadkhodazadeh, Mahdi Korean Academy of Periodontology 2013 Journal of Periodontal & Implant Science Vol.43 No.5
Purpose: This study aimed to assess the combined effect of dismantling before sterilization and aging on the accuracy (${\pm}10%$ of the target torque) of spring-style mechanical torque devices (S-S MTDs). Methods: Twenty new S-SMTDs from two different manufacturers (Nobel Biocare and Straumann: 10 of each type) were selected and divided into two groups, namely, case (group A) and control (group B). For sterilization, 100 cycles of autoclaving were performed in 100 sequences. In each sequence, 10 repetitions of peak torque values were registered for aging. To measure and assess the output of each device, a Tohnichi torque gauge was used (P<0.05). Results: Before steam sterilization, all of the tested devices stayed within 10% of their target values. After 100 cycles of steam sterilization and aging with or without dismantling of the devices, the Nobel Biocare devices stayed within 10% of their target torque. In the Straumann devices, despite the significant difference between the peak torque and target torque values, the absolute error values stayed within 10% of their target torque. Conclusion: Within the limitations of this study, there was no significant difference between the mean and absolute value of error between Nobel Biocare and Straumann S-S MTDs.
Substrate Construes the Copper and Nickel Ions Impacts on the Mushroom Tyrosinase Activities
Gheibi, N.,Saboury, A.A.,Haghbeen, K. Korean Chemical Society 2006 Bulletin of the Korean Chemical Society Vol.27 No.5
Mushroom tyrosinase (MT) structural changes in the presence of $Cu ^{2+}$ and $Ni ^{2+}$ were studied separately. Far-UV CD spectra of the incubated MT with the either of the metal ions indicated reduction of the well-ordered secondary structure of the enzyme. Increasing in the maximum fluorescence emission of anilinonaphthalene-8-sulfonic acid (ANS) was also revealing partial unfolding caused by the conformational changes in the tertiary structure of MT. Thermodynamic studies on the chemical denaturation of MT by dodecyl trimethylammonium bromide (DTAB) showed decrease in the stability of MT in the presence of $Cu ^{2+}$ or $Ni ^{2+}$ using their activation concentrations. Both activities of MT were also assessed in the presence of different concentrations of these ions, separately, with various monophenols and their corresponding diphenols. Kinetic studies revealed that cresolase activity on p-coumaric acid was boosted in the presence of either of the metal ions, but inhibited when phenol, L-tyrosine, or 4-[(4-methylphenyl)azo]-phenol was substrate. Similarly, catecholase activity on caffeic acid was enhanced in the presence of $Cu ^{2+}$ or $Ni ^{2+}$, but inhibited when catechol, L-DOPA, or 4-[(4-methylbenzo)azo]-1,2-benzenediol was substrate. Results of this study suggest that both cations make MT more fragile and less active. However, the effect of the substrate structure on the MT allosteric behavior can not be ignored.
Temperature Dependence of Activation and Inhibition of Mushroom Tyrosinase by Ethyl Xanthate
Alijanianzadeh, M.,Saboury, A.A. Korean Chemical Society 2007 Bulletin of the Korean Chemical Society Vol.28 No.5
A new alkyldithiocarbonate (xanthate), as sodium salts, C2H5OCS2Na, was synthesized by the reaction between CS2 with ethyl alcohol in the presence of NaOH. The new xanthate was characterized by 1H NMR, IR and elemental analysis. Then, the new synthesized compound was examined for functional study of cresolase activity of Mushroom Tyrosinase (MT) from a commercial source of Agricus bisporus in 10 mM phosphate buffer pH 6.8, at three temperatures of 10, 20 and 33℃ using UV spectrophotemetry. 4-[(4-methylphenyl)- azo]-phenol (MePAPh) was used as a synthetic substrate for the enzyme for cresolase reaction. The results show that ethyl xanthate can activate or inhibit the cresolase activity of mushroom tyrosinase depending to the concentration of ethyl xanthate. It was concluded that the enzyme has two distinct sites for ethyl xanthate. The first one is a high-affinity activation site and the other is a low-affinity inhibition site. Activation of the enzyme in the low concentration of ethyl xanthate arises from increasing the affinity of binding for the substrate as well as increasing the enzyme catalytic constant. The affinity of ligand binding in the activation site is decreased by increasing of the temperature, which is the opposite result for the inhibition site. Hence, the nature of the interaction of ethyl xanthate is different in two distinct sites. The binding process for cresolase inhibition is only entropy driven, meanwhile the binding process for cresolase activation is not only entropy driven but also enthalpy driven means that hydrophobic interaction is more important in the inhibition site.
Hekmat, A.,Saboury, A. A.,Divsalar, A.,Khanmohammadi, M. Korean Chemical Society 2008 Bulletin of the Korean Chemical Society Vol.29 No.8
Results of intrinsic and extrinsic fluorescence studies on choline oxidase revealed that the enzyme at high alkaline pH values has more accessible hydrophobic patches relative to acidic pH. Fluorescence quenching studies with acrylamide confirm these changes. The quenching constants were also determined at different pH(s) by using the Stern-Volmer equation. CD studies showed that at higher pH a transition from $\alpha$-helix to $\beta$- structure was appeared while at lower pH the content of $\alpha$-helix structure was increased. Furthermore, analysis of the spectral data using chemometric method gave evidence for existence of intermediate components at very high pH(s). Results of thermal denaturation evaluated that the enzyme has the most instability at higher pH(s). Altogether low and high pH values caused significant alteration on secondary and tertiary structures of choline oxidase via inducing of an intermediate.