Lactoperoxidase-catalyzed oxidation of thiocyanate: polarographic study of the oxidation products.
Lactoperoxidase-catalyzed oxidation of thiocyanate: polarographic study of the oxidation products.
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DOI：
10.1021/bi00532a023
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发表时间：
1982-02
期刊：
影响因子：
2.9
通讯作者：
K. Pruitt;J. Tenovuo;R. W. Andrews;T. McKane
中科院分区：
文献类型：
--
作者：
K. Pruitt;J. Tenovuo;R. W. Andrews;T. McKane
用直流极谱法和线性扫描伏安法研究了乳过氧化物酶催化硫氰酸根（SCN-）氧化反应。在pH6.5时，主要氧化产物为次硫氰酸根（OSCN-），半波电位（E1/2）为-0.39 ~-0.44V。OSCN的E1/2-在文献中不可用。OSCN-的鉴定是基于OSCN-峰的电流与化学测定的OSCN-浓度之间的密切相关性。此外，具体的衰减率的电流和化学检测OSCN-是相似的，两条曲线遵循表观一级动力学。随后，添加还原剂（2-巯基乙醇）导致在两个化学检测的OSCN-和OSCN-波的极谱图中立即消失。产生OSCN-峰需要乳过氧化物酶（LPO）系统的所有三种组分（SCN-、H2 O2和LPO）。向OSCN--SCN-混合物中加入过量的H_2O_2或H_2O_2-LPO，导致形成特征峰电位（Ep）为-0.20至-0.25 V的新峰。该新峰的产生与OSCN-浓度的同时显著增强的降低有关，表明H_2O_2（或H_2O_2-LPO）与OSCN-之间可能发生反应。通过单独添加缓冲液未获得等效反应。这个新峰可能代表SCN-的高级含氧酸（O2 SCN-，O3 SCN-），其形成于OSCN-被H2 O2或H2 O2-LPO氧化。这种类型的反应可以解释为什么在已经含有OSCN-的溶液中（例如，在唾液中），H2 O2的加入导致除了OSCN-之外的高反应性、短寿命的抗微生物产物的形成。
The lactoperoxidase-catalyzed oxidation of thiocyanate (SCN-) was studied by two different polarographic techniques: direct current polarography and linear sweep voltammetry. The main oxidation product at pH 6.5, with a half-wave potential (E1/2) of -0.39 to -0.44 V, was identified as hypothiocyanite (OSCN-) ion. The E1/2 for OSCN- was not available in the literature. The identification of OSCN- was based on a close correlation between the current of the OSCN- peak and the concentration of chemically assayed OSCN-. Also the specific rates of decay of the current and that of chemically detectable OSCN- were similar, and both curves followed apparent first-order kinetics. Subsequently, the addition of a reducing agent (2-mercaptoethanol) resulted in immediate disappearance of both chemically detectable OSCN- and the OSCN- wave in the polarograms. All three components of the lactoperoxidase (LPO) system (SCN-, H2O2, and LPO) were needed to produce the OSCN- peak. Addition of excess H2O2 or H2O2-LPO to an OSCN--SCN- mixture resulted in a formation of a new peak with a characteristic peak potential (Ep) of -0.20 to -0.25 V. The generation of this new peak was associated with a simultaneous, markedly enhanced decrease of OSCN- concentration, indicating a possible reaction between H2O2 (or H2O2-LPO) and OSCN-. No equivalent reaction was obtained by the addition of buffer alone. This new peak may represent higher oxy acids of SCN- (O2SCN-, O3SCN-), formed in the oxidation of OSCN- by H2O2 or by H2O2-LPO. This type of reaction can explain why, in solutions which already contain OSCN- (e.g., in saliva), the addition of H2O2 results in the formation of highly reactive, short-lived antimicrobial products in addition to OSCN-.