Huber R E, Edwards L A, Carne T J
Division of Biochemistry, Faculty of Science, University of Calgary, Alberta, Canada.
J Biol Chem. 1989 Jan 25;264(3):1381-6.
Studies with lactoperoxidase showed that a highly reactive intermediate is produced (on the enzyme) from I- and H2O2 which then diffuses from the enzyme and very rapidly and indiscriminately iodinates any Tyr or peptides containing Tyr which are in the same solution. The evidence supporting these conclusions follows. 1) The rate followed the Michaelis-Menten pattern with I- and H2O2 while the concentration of Tyr peptides had no measurable effect on the rate; 2) the rates of reaction were independent of the type of peptide in which Tyr was located; 3) the amount of iodination which had occurred after the reaction had gone to completion and the amounts of monoiodination and diiodination after completion of the reaction were independent of the peptide type, the pH, the solvent polarity, or the ionic strength; 4) competition for reaction by two very different Tyr peptides depended only on their initial concentrations; and 5) iodination of a large protein occurred through a dialysis membrane. Free Tyr was iodinated at the same rate as Tyr peptides by lactoperoxidase, but monoiodotyrosine and m-fluorotyrosine were iodinated at one-half that rate. The results also showed that one can choose ratios of [peptide] to [H2O2] such that monoiodination is maximized relative to diiodination. It was also found that the iodination capacity of a mixture of I- and H2O2 with lactoperoxidase (when Tyr was absent) was only slowly dissipated. Finally, the results showed that lactoperoxidase can be used to brominate and chlorinate Tyr peptides at a slow rate.
对乳过氧化物酶的研究表明，碘离子（I⁻）和过氧化氢（H₂O₂）在该酶上会产生一种高活性中间体，此中间体随后从酶上扩散出来，并非常迅速且无差别地对同一溶液中任何含酪氨酸（Tyr）的酪氨酸或肽进行碘化。支持这些结论的证据如下：1）反应速率遵循米氏动力学模式，与碘离子和过氧化氢有关，而酪氨酸肽的浓度对反应速率没有可测量的影响；2）反应速率与酪氨酸所在肽的类型无关；3）反应完成后发生的碘化量以及反应完成后的单碘化和二碘化量与肽的类型、pH、溶剂极性或离子强度无关；4）两种非常不同的酪氨酸肽对反应的竞争仅取决于它们的初始浓度；5）一种大蛋白质通过透析膜发生碘化。乳过氧化物酶对游离酪氨酸的碘化速率与对酪氨酸肽的碘化速率相同，但对单碘酪氨酸和间氟酪氨酸的碘化速率仅为其一半。结果还表明，可以选择肽与过氧化氢的比例，以使相对于二碘化，单碘化最大化。还发现，当不存在酪氨酸时，碘离子和过氧化氢与乳过氧化物酶的混合物的碘化能力仅缓慢消散。最后，结果表明乳过氧化物酶可用于以缓慢的速率对酪氨酸肽进行溴化和氯化。
