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2 Acta Biochimica Polonica

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Effects of pH on the activity and structure of choline oxidase from Alcaligenes species

100%

Hekmat A. , Saboury A. A. , Moosavi-Movahedi A. A. , Ghourchian H. , Ahmad F.

nr 3

549-557

A reversible effect of pH on the ionization of amino-acid residues at the active center of choline oxidase was observed near the optimum pH (8). Inactivation of choline oxidase took place in the pH ranges 3–6 and 9–11, in which irreversible changes in the structure occur leading to the enzyme inactivation. The first order rate constants of the enzyme’s inactivation at various pH values were estimated for the irreversible changes. The Arrhenius analysis revealed no significant changes in the activation enthalpy, while an increase in the activation entropy reflected an increase in the conformational freedom.

Inhibition study of adenosine deaminase by caffeine using spectroscopy and isothermal titration calorimetry

86%

Saboury A. A. , Divsalar A. , Ataie G. , Amanlou M. , Moosavi-Movahedi A. A. , Hakimelahi G. H.

nr 3

Kinetic and thermodynamic studies were made on the effect of caffeine on the activity of adenosine deaminase in 50 mM sodium phosphate buffer, pH 7.5, using UV spectrophotometry and isothermal titration calorimetry (ITC). An uncompetitive inhibition was observed for caffeine. A graphical fitting method was used for determination of binding constant and enthalpy of inhibitor binding by using isothermal titration microcalorimetry data. The dissociation-binding constant is equal to 350 uM by the microcalorimetry method, which agrees well with the value of 342 uM for the inhibition constant that was obtained from the spectroscopy method. Positive dependence of caffeine binding on temperature indicates a hydrophobic interaction.