title: Kinetic studies on the oxidation of nitrite by horseradish peroxidase and lactoperoxidase.
abstract: The reaction of nitrite (NO2-) with horseradish peroxidase and lactoperoxidase was studied. Sequential mixing stopped-flow measurements 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(-1) dm3 s(-1) and 3.5 +/- 0.05 x 10(4) mol(-1) dm3 s(-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 of 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-. NO2- did not influence the activity measurements of horseradish peroxidase by ABTS or guaiacol method.
authors.affiliation: Institute of Applied Radiation Chemistry, Technical University of Lódź, Poland. lgebicka@mitr.p.lodz.pl
authors.forename: L
authors.initials: L
authors.lastname: Gebicka
mesh_terms: D052160:Benzothiazoles; D006139:Guaiacol / Q000737:chemistry / Q000378:metabolism; D006735:Horseradish Peroxidase / Q000378:metabolism*; D007700:Kinetics; D007784:Lactoperoxidase / Q000378:metabolism*; D009573:Nitrites / Q000737:chemistry / Q000378:metabolism*; D010084:Oxidation-Reduction; D013053:Spectrophotometry; D013451:Sulfonic Acids / Q000737:chemistry / Q000378:metabolism
chemical_list: D052160:Benzothiazoles; D009573:Nitrites; D013451:Sulfonic Acids; C002502:2,2'-azino-di-(3-ethylbenzothiazoline)-6-sulfonic acid; D006139:Guaiacol; D006735:Horseradish Peroxidase; D007784:Lactoperoxidase