Wever R, Kast W M, Kasinoedin J H, Boelens R
Biochim Biophys Acta. 1982 Dec 20;709(2):212-9. doi: 10.1016/0167-4838(82)90463-0.
Peroxidation of SCN- to OSCN-, catalysed by myeloperoxidase and lactoperoxidase, was studied. The rate of this reaction showed sharp optima between pH 5 and 7.5, the position of which is determined by the concentrations of both SCN- and H2O2. At low pH values, both SCN- and H+ inhibited myeloperoxidase and lactoperoxidase competitively with respect to H2O2. The inhibition constants of SCN- for myeloperoxidase and lactoperoxidase (2 and 6 mM, respectively) are independent of pH. For these enzymes a Ki for H+ of 1 microM was found that corresponded to an ionisable group on the enzymes (pKa = 6) which controls the enzymic activity. A kinetic expression is proposed that explains most of the data. The physiological consequences of the corresponding mechanism are discussed.
研究了由髓过氧化物酶和乳过氧化物酶催化的硫氰酸盐（SCN-）过氧化生成次硫氰酸盐（OSCN-）的反应。该反应速率在pH 5至7.5之间呈现出明显的最佳值，其位置由SCN-和过氧化氢（H2O2）的浓度决定。在低pH值下，SCN-和H+相对于H2O2竞争性抑制髓过氧化物酶和乳过氧化物酶。SCN-对髓过氧化物酶和乳过氧化物酶的抑制常数（分别为2 mM和6 mM）与pH无关。对于这些酶，发现H+的抑制常数（Ki）为1 microM，这对应于酶上一个控制酶活性的可电离基团（pKa = 6）。提出了一个动力学表达式来解释大部分数据。讨论了相应机制的生理后果。
