title: Kinetics and thermal stability of two peroxidase isozymes from Eupatorium odoratum.
abstract: The Eupatorium odoratum leaf peroxidase exists as at least seven distinct isozymes (three cationic, three anionic, and one neutral). These isozymes were identified and separated by preparative iso-electric focusing. Thermal stability, including the activation enthalpy (deltaH*), free energy of inactivation (deltaG*) and activation entropy (deltaS*), and kinetic studies of two isozymes, one having a pI of 5.0 (E5) and another one having a pI of 7.0 (E7) with mol mass of 43 and 50 kD, respectively, were studied in detail. Of the molecular weight of E5 and E7, 25 and 32% correspond to the carbohydrate content of the isozymes. Optimal pH was in the acidic range of 3.6-3.8 for E5 and 3.8 for E7 with the oxidation of ABTS. E7 and E5 showed activation energy for inactivation, 194.8 and 145.4 kJ/mol, respectively. Both the isozymes showed distinct substrate specificity. The catalytic specificity constant for E5 and E7 were 112 x 105 and 124 x 105/s.M, respectively, when 2,2'-azino-bis-(3-ethylbenz-thiazoline-6 sulfonic acid) was used as the substrate. Maximum affinity (i.e., lowest Km value) to H2O2 was shown by E5 and E7 along with Pyrogallol and was 0.02 and 0.05/s.M, respectively.
authors.affiliation: Polymer Science, Chemical Sciences Division, Regional Research Laboratory (CSIR), Trivandrum 695 019, India.
authors.forename: D Nisha
authors.initials: DN
authors.lastname: Rani
authors.forename: T Emilia
authors.initials: TE
authors.lastname: Abraham
mesh_terms: D052160:Benzothiazoles; D002384:Catalysis; D036604:Chromolaena / Q000201:enzymology*; D019277:Entropy; D004795:Enzyme Stability; D006358:Hot Temperature; D006861:Hydrogen Peroxide / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D007526:Isoelectric Point; D007527:Isoenzymes / Q000378:metabolism*; D007700:Kinetics; D008970:Molecular Weight; D009195:Peroxidase / Q000378:metabolism*; D011748:Pyrogallol / Q000378:metabolism; D013379:Substrate Specificity; D013451:Sulfonic Acids / Q000737:chemistry; D013997:Time Factors
chemical_list: D052160:Benzothiazoles; D007527:Isoenzymes; D013451:Sulfonic Acids; D011748:Pyrogallol; C002502:2,2'-azino-di-(3-ethylbenzothiazoline)-6-sulfonic acid; D006861:Hydrogen Peroxide; D009195:Peroxidase