کد مقاله | کد نشریه | سال انتشار | مقاله انگلیسی | نسخه تمام متن |
---|---|---|---|---|
1177186 | 961957 | 2008 | 6 صفحه PDF | دانلود رایگان |
![عکس صفحه اول مقاله: A colorimetric assay for steady-state analyses of iodo- and bromoperoxidase activities A colorimetric assay for steady-state analyses of iodo- and bromoperoxidase activities](/preview/png/1177186.png)
The standard assay for iodoperoxidase activity is based on the spectrophotometric detection of triiodide formed during the enzymatic reaction. However, chemical instability of I3- has limited the method to high iodide concentrations and acidic conditions. Here we describe a simple spectrophotometric assay for the determination of iodoperoxidase activities of vanadium haloperoxidases based on the halogenation of thymol blue. The relation between color and chemical entities produced by the vHPO/H2O2/I− catalytic system was characterized. The method was extended to bromine and, for the first time, allowed measurement of both iodo- and bromoperoxidase activities using the same assay. The kinetic parameters (Km and kcat) of bromide and iodide for vanadium bromoperoxidase from Ascophyllum nodosum were determined at pH 8.0 from steady-state kinetic analyses. The results are concordant with an ordered two-substrate mechanism. It is proposed that halide selectivity is guided by the chemical reactivity of peroxovanadium intermediate rather than substrate binding. This method is superior to the standard I3- assay, and we believe that it will find applications for the characterization of other vanadium as well as heme haloperoxidases.
Journal: Analytical Biochemistry - Volume 379, Issue 1, 1 August 2008, Pages 60–65