MacLatchy D L, Eales J G
Department of Zoology, University of Manitoba, Winnipeg, Canada.
Gen Comp Endocrinol. 1992 May;86(2):313-22. doi: 10.1016/0016-6480(92)90116-2.
L-Thyroxine (T4) 5'-monodeiodinase (5'D) activity was examined in the microsomal fractions of liver, kidney, gill, white skeletal muscle, and red blood cells (RBC) of fed rainbow trout held in freshwater at 12 degrees. Two distinct 5'D systems were established and were examined at low (0.08-1.3 nM) or high (1.6-25 nM) T4 substrate ranges. The low substrate 5'D occurred in liver, gill, and muscle, but not in kidney or RBC. The pH optimum was 7.0 and the optimum dithiothreitol (DTT) level ranged from 7 to 10 mM. The Km values (nM) were liver, 0.098; muscle, 0.198; and gill, 0.168. The Vmax values (pmol.hr-1.mg protein-1) were liver, 3.74; muscle, 0.79; and gill, 0.62. DTT affected both the Vmax and the Km, and propylthiouracil (PTU) inhibited the Vmax. These data suggest a ping-pong type mechanism. In contrast, the high substrate 5'D occurred only in liver (pH 7 optimum, DTT optimum 15 mM) and in kidney (pH optima 6 and 8, DTT optimum 15 mM). The Km values (nM) were liver, 10.0; and kidney, 14.7; the Vmax values (pmol.hr-1.mg protein-1) were liver, 8.21; and kidney, 5.76. DTT affected the Vmax but not the Km and PTU did not inhibit, indicating a sequential type mechanism. In conclusion, in rainbow trout there are at least two types of 5'D which differ in their tissue distribution, T4 substrate affinity, and enzyme mechanism, and which do not resemble in their combined properties the 5'D forms established in higher vertebrate taxa.
对饲养在12摄氏度淡水中的虹鳟鱼的肝脏、肾脏、鳃、白色骨骼肌和红细胞（RBC）的微粒体部分中的L-甲状腺素（T4）5'-单脱碘酶（5'D）活性进行了检测。建立了两种不同的5'D系统，并在低（0.08 - 1.3 nM）或高（1.6 - 25 nM）T4底物范围内进行检测。低底物5'D存在于肝脏、鳃和肌肉中，而不存在于肾脏或红细胞中。最适pH为7.0，最适二硫苏糖醇（DTT）水平为7至10 mM。Km值（nM）分别为：肝脏，0.098；肌肉，0.198；鳃，0.168。Vmax值（pmol·hr⁻¹·mg蛋白质⁻¹）分别为：肝脏，3.74；肌肉，0.79；鳃，0.62。DTT对Vmax和Km均有影响，丙硫氧嘧啶（PTU）抑制Vmax。这些数据表明其为乒乓型机制。相比之下，高底物5'D仅存在于肝脏（最适pH 7，最适DTT 15 mM）和肾脏（最适pH 6和8，最适DTT 15 mM）中。Km值（nM）分别为：肝脏，10.0；肾脏，14.7；Vmax值（pmol·hr⁻¹·mg蛋白质⁻¹）分别为：肝脏，8.21；肾脏，5.76。DTT影响Vmax但不影响Km，PTU不产生抑制作用，表明其为顺序型机制。总之，虹鳟鱼中至少存在两种类型的5'D，它们在组织分布、T4底物亲和力和酶机制方面存在差异，并且其综合特性与高等脊椎动物类群中建立的5'D形式不同。
