A kinetic study of the oxidation of hydroxamic acids by compounds I and II of horseradish peroxidase: Effect of transition metal ions

• Published in: Journal of coordination chemistry Vol. 71; no. 11-13; pp. 1728 - 1737
• Main Authors: Samuni, Uri, Maimon, Eric, Goldstein, Sara
• Format: Journal Article
• Language: English
• Published: Abingdon Taylor & Francis 03.07.2018; Taylor & Francis Ltd
• Subjects: Acetohydroxamic acid; Coordination compounds; HNO; HRP; Hydrogen peroxide; III; Ions; Metal ions; Oxidation; Oxidation rate; Peroxidase; Reaction kinetics; SAHA; suberohydroxamic acid; Transition metals
• ISSN: 0095-8972; 1029-0389
• DOI: 10.1080/00958972.2018.1493200

Oxidation of hydroxamic acids (HXs) generates HNO, and it is not clear whether it is formed also in the presence of metal ions. The kinetics of the oxidation of HXs, such as acetohydroxamic acid, suberohydroxamic acid, and suberoylanilide hydroxamic acid (SAHA), by compounds I and II of horseradish peroxidase (HRP) at pH 7.0 and 25 °C have been studied using rapid-mixing stopped-flow. The kinetics of these reactions were compared to those observed in the presence of Cu(ClO 4 ) 2 , NiSO 4 , or ZnSO 4 . The rates decrease upon increasing [Cu II ] at constant [HXs], and no oxidation of HX occurs when [HX]/[Cu II ] ≈ 2, implying that HX oxidation in the presence of Cu II proceeds through the free ligand since the predominant complex is CuX 2 . In the case of Ni II , the oxidation rate decreases upon increasing the ratio [Ni II ]/[HX] beyond 1, where the predominant complex is Ni II X + , implying that its oxidation is feasible. The effect of Zn II could be studied only on the rate of HXs oxidation by compound II demonstrating similar behavior to that of Ni II . HXs were also oxidized catalytically by HRP/H 2 O 2 at pH 7.0, demonstrating that metal ions facilitate the formation of HNO while hardly affecting its yield and the extent of HX oxidation.