Ohlsson P I
Eur J Biochem. 1984 Jul 16;142(2):233-8. doi: 10.1111/j.1432-1033.1984.tb08276.x.
The dithionite ion is catalytically disproportionated by lactoperoxidase with Km = 0.36 mM in 100 mM glycine HCl pH 3.0. The products formed are thiosulfate and hydrogensulfite ions. The rate of reaction is considerably increased at low pH with a pKa at 3-3.5 possibly indicating the involvement of a carboxyl group. The reaction is competitively inhibited by hydrogensulfite, Ki = 5.5 mM in 100 mM glycine HCl pH 3.50. Four different spectral forms of reduced lactoperoxidase appear during the reaction. The first two forms are found during the lag phase of the reaction. The third form, which is interpreted as a ternary complex, exists under the dismutation phase. After exhaustion of the substrate a visible spectrum similar to that of lactoperoxidase H2O2 compound III appears. A mechanistic model for the lactoperoxidase dismutation of the dithionite ion is proposed and discussed.
连二亚硫酸根离子在100 mM甘氨酸盐酸盐pH 3.0条件下被乳过氧化物酶催化歧化，米氏常数Km = 0.36 mM。生成的产物是硫代硫酸根离子和亚硫酸氢根离子。在低pH值下反应速率显著增加，pKa为3 - 3.5，这可能表明有羧基参与。该反应受到亚硫酸氢根的竞争性抑制，在100 mM甘氨酸盐酸盐pH 3.50条件下抑制常数Ki = 5.5 mM。反应过程中出现四种不同光谱形式的还原型乳过氧化物酶。前两种形式出现在反应的延迟阶段。第三种形式被解释为三元复合物，存在于歧化阶段。底物耗尽后，出现与乳过氧化物酶H2O2化合物III相似的可见光谱。提出并讨论了乳过氧化物酶催化连二亚硫酸根离子歧化的机理模型。
