Acta Biochimica Polonica, 46(4), 919-927, Review

Kinetic studies on the oxidation of nitrite by horseradish peroxidase and lactoperoxidase

Lidia Gębicka^e-mail

Institute of Applied Radiation Chemistry, Technical University of Łódź, W. Wróblewskiego 15, 93-950 Łódź, Poland

 Received: 14 October 1999

Key words: horseradish peroxidase, lactoperoxidase, nitrite, stopped-flow,

 The reaction of nitrite (NO^-₂) with horseradish peroxidase and lactoperoxidase was studied. Sequential mixing sopped-flow measeruments gave the following values for the rate constants of the reaction of nitrite with compounds II (oxoferryl heme intermediates) of horseradish peroxidase and lactoperoxidase at pH 7.0, 13.3 ± 0.07 mol^-1dm³s^-1 and 3.5 ± 0.05 · 10⁴mol^-1dm³s^-1, respectively. Nitrite, at neutral pH, influenced measurements of activity of lactoperoxidase with typical substrates like 2,2'-azino-bis[ethyl-benzothiazoline-(6)-sulphonic acid] (ABTS), guaiacol or thiocyanate (SCN^-). The rate of ABTS and guaiacol oxidation increased linearly with nitrite concentration up to 2.5-5 mmol dm^-3. On the other hand, two-electron SCN^- oxidation was inhibited in the presence od nitrite. Thus, nitrite competed with the investigated substrates of lactoperoxidase. The intermediate, most probably nitrogen dioxide (^*NO₂), reacted more rapidly with ABTS or guaiacol than did lactoperoxidase compound II. It did not, however, effectively oxidize SCN^- to OSCN^-. NO^-₂ did not influence the activity measurements of horseradish peroxidase by ABTS or guaiacol method.

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