Goswami A, Rosenberg I N
Department of Medicine, Framingham Union Hospital, Massachusetts 01701.
Biochem Int. 1989 Aug;19(2):361-8.
Although all iodothyronine 5'-deiodinases require thiol cofactors for activity, the type II variant has been suspected to contain no reactive thiol groups because of its resistance to inactivation by iodoacetate (IAC). We report here that, under suitable stoichiometric conditions for the alkylation reaction, the type II enzyme is substantially inactivated by IAC. The reaction follows pseudo-first-order kinetics with an inactivation rate constant of 0.08 min-1. Moreover, the enzyme is inhibited by hydroxyethyl disulfide and propylthiouracil. These reagents, but not thyroxine, also protect the enzyme from inactivation by IAC, The data suggest that IAC interacts with an essential thiol group in the active center domain.
尽管所有的碘甲状腺原氨酸5'-脱碘酶都需要硫醇辅因子来发挥活性，但由于II型变体对碘乙酸（IAC）的失活作用具有抗性，因此一直怀疑它不含有反应性硫醇基团。我们在此报告，在适合烷基化反应的化学计量条件下，II型酶会被IAC大量失活。该反应遵循假一级动力学，失活速率常数为0.08 min-1。此外，该酶会被羟乙基二硫化物和丙硫氧嘧啶抑制。这些试剂（而非甲状腺素）也能保护该酶不被IAC失活。数据表明，IAC与活性中心结构域中的一个必需硫醇基团相互作用。
