Francisco García-Cánovas

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H2O2 is the usual oxidizing substrate of horseradish peroxidase C (HRP-C). In the absence in the reaction medium of a one-electron donor substrate, H2O2 is able to act as both oxidizing and reducing substrate. However, under these conditions the enzyme also undergoes a progressive loss of activity. There are several pathways that maintain the activity of(More)
The inactivation of horseradish peroxidase A2 (HRP-A2) with H2O2 as the sole substrate has been studied. In incubation experiments it was found that the fall in HRP-A2 activity was non-linearly dependent on H2O2 concentrations and that a maximum level of inactivation of approximately 80% (i.e. ∼ 20% residual activity) was obtained with 2000 or more(More)
A continuous spectrophotometric method for the rapid determination of monophenolase activity of tyrosinase is described. This method is based on the coupling reaction between 3-methyl-2-benzothiazolinone hydrazone (MBTH) and the quinone products of the oxidation of various monophenols in the presence of tyrosinase. The chemical reaction between MBTH and(More)
A procedure for calibrating a Clark-type oxygen electrode is described. This method is based on the oxidation of 4-tert-butylcatechol (TBC) by O2 catalyzed by tyrosinase, to yield 4-tert-butyl-o-benzoquinone (TBCQ). This reaction consumes known amounts of oxygen in accordance with the stoichiometry: 2TBC + O2----2TBCQ + 2H2O and can be used to determine the(More)
The effect of ascorbic acid on the monophenolase activity of tyrosinase, using tyrosine as substrate, has been studied. Over the ranges of ascorbic acid concentration used, no direct effect on the enzyme is found. However, a shortening of the characteristic induction period of the hydroxylation reaction is observed. The evolution of the reaction is(More)
Tyrosinase is a copper enzyme with broad substrate specifity toward a lot of phenols with different biotechnological applications. The availability of quick and reliable measurement methods of the enzymatic activity of tyrosinase is of outstanding interest. A series of spectrophotometric methods for determining the monophenolase and diphenolase activities(More)
A sensitive colorimetric method for naringin estimation using 2,2'-azino-bis-(3-ethylbenzthiazoline-6-sulfonic acid) (ABTS) as peroxidase substrate is described. The method is based on the coupling reaction of an ABTS radical cation with an oxidation product of naringin formed by peroxidase. This coupling reaction leads to the formation of a purple-colored(More)
In the absence of reductant substrates, and with excess H2O2, peroxidase (donor: hydrogen-peroxide oxidoreductase, EC shows the kinetic behaviour of a suicide inactivation, H2O2 being the suicide substrate. From the complex (compound I-H2O2), a competition is established between two catalytic pathways (the catalase pathway and the compound(More)
The mechanism of the reaction of horseradish peroxidase isoenzyme C (HRPC) with hydrogen peroxide to form the reactive enzyme intermediate compound I has been studied using electronic absorbance, rapid-scan stopped-flow, and electron paramagnetic resonance (EPR) spectroscopies at both acid and basic pH. The roles of the active site residues His42 and Arg38(More)