Department of Chemistry and Biomolecular Sciences, Macquarie University, North Ryde, New South Wales, Australia.
J Neurochem. 2011 Aug;118(3):379-87. doi: 10.1111/j.1471-4159.2011.07220.x. Epub 2011 Mar 15.
Ketimine reductase (E.C. 1.5.1.25) was purified to apparent homogeneity from lamb forebrain by means of a rapid multi-step chromatography protocol. The purified enzyme was identified by MS/MS (mass spectrometry) as μ-crystallin. The identity was confirmed by heterologously expressing human μ-crystallin in Escherichia coli and subsequent chromatographic purification of the protein. The purified human μ-crystallin was confirmed to have ketimine reductase activity with a maximum specific activity similar to that of native ovine ketimine reductase, and was found to catalyse a sequential reaction. The enzyme substrates are putative neuromodulator/transmitters. The thyroid hormone 3,5,3'-l-triiodothyronine (T3) was found to be a strong reversible competitive inhibitor, and may have a novel role in regulating their concentrations. μ-Crystallin is also involved in intracellular T3 storage and transport. This research is the first to demonstrate an enzyme function for μ-crystallin. This newly demonstrated enzymatic activity identifies a new role for thyroid hormones in regulating mammalian amino acid metabolism, and a possible reciprocal role of enzyme activity regulating bioavailability of intracellular T3.
酮还原酶（EC 1.5.1.25）通过快速的多步色谱法从羊前脑纯化到近乎同质。通过 MS/MS（质谱）鉴定纯化的酶为微晶体蛋白。通过在大肠杆菌中异源表达人微晶体蛋白并随后对蛋白质进行色谱纯化来确认身份。纯化的人微晶体蛋白被证实具有酮还原酶活性，最大比活性与天然绵羊酮还原酶相似，并且发现它催化顺序反应。该酶的底物是假定的神经调节剂/递质。甲状腺激素 3,5,3'-l-三碘甲状腺原氨酸（T3）被发现是一种强的可逆竞争性抑制剂，可能在调节它们的浓度方面具有新的作用。微晶体蛋白还参与细胞内 T3 的储存和运输。这项研究首次证明了微晶体蛋白的酶功能。这种新证明的酶活性确定了甲状腺激素在调节哺乳动物氨基酸代谢中的新作用，以及酶活性调节细胞内 T3 生物利用度的可能相互作用。
