Zhou J, Weiner H
Department of Biochemistry, Purdue University, West Lafayette, USA.
Eur J Biochem. 1997 Apr 1;245(1):123-8. doi: 10.1111/j.1432-1033.1997.00123.x.
A fragment of a cytosolic thyroid-hormone-binding protein from Xenopus liver was reported to be 92-100% identical to residues 236-258 in several cytosolic aldehyde dehydrogenases [Yamauchi, K. & Tata, J. R. (1994) Eur. J. Biochem. 225, 1105-1112], which have been proposed to form part of the hinge region necessary to bind the adenosine moiety of NAD. Here we investigated the effects of two thyroxine analogs, 3,3',5-triiodo-L-thyronine and 3,3',5-triiodothyroacetic acid, on purified human liver mitochondrial and cytosolic aldehyde dehydrogenases. The compounds were found to be competitive inhibitors against NAD and uncompetitive inhibitors with respect to aldehyde. At pH 7.4, the apparent Ki values were in the micromolar range when the concentration of NAD was varied. The inhibition against recombinantly expressed mutant forms of aldehyde dehydrogenase, which possessed diminished NAD binding, was determined. Essentially no differences were found between the native enzyme and the mutants, showing that the analog binding was not affected by altering the NAD-binding site. Furthermore, the analogs could displace NAD but not NADH from the enzyme. These findings indicated that the binding of NAD differed from that of NADH, and that aldehyde dehydrogenases, like other dehydrogenases, can be inhibited by thyroxine analogs.
据报道，非洲爪蟾肝脏胞质甲状腺激素结合蛋白的一个片段与几种胞质醛脱氢酶的236 - 258位残基有92 - 100%的同一性[山内，K. & 塔塔，J. R. (1994) 《欧洲生物化学杂志》225, 1105 - 1112]，这些残基被认为构成了结合NAD腺苷部分所需的铰链区的一部分。在此，我们研究了两种甲状腺素类似物，3,3',5 - 三碘 - L - 甲状腺原氨酸和3,3',5 - 三碘甲状腺乙酸，对纯化的人肝脏线粒体和胞质醛脱氢酶的影响。发现这些化合物是NAD的竞争性抑制剂和醛的非竞争性抑制剂。在pH 7.4时，当NAD浓度变化时，表观Ki值在微摩尔范围内。测定了对重组表达的醛脱氢酶突变体形式的抑制作用，这些突变体的NAD结合能力减弱。在天然酶和突变体之间基本没有发现差异，表明类似物的结合不受NAD结合位点改变的影响。此外，这些类似物可以从酶上取代NAD但不能取代NADH。这些发现表明NAD的结合与NADH的结合不同，并且醛脱氢酶与其他脱氢酶一样，可以被甲状腺素类似物抑制。
