2-Thiouracil (Thiouracil) is an antithyroid compound. 2-Thiouracil is a selective inhibitor of neuronal nitric oxide synthase (nNOS) with a Ki of 20 μM. The drug apparently interfered with the substrate- and tetrahydrobiopterin (BH(4))-binding to the enzyme. It caused a 60% inhibition of H(2)O(2) production in the absence of L-arginine and BH(4), and antagonised BH(4)-induced dimerisation of nNOS, but did not affect cytochrome c reduction[3]. 2-thiouridine (alone or within an RNA chain) is predominantly transformed under oxidative stress conditions to 4-pyrimidinone riboside (H2U) and not to uridine. 2-Thiouracil-containing nucleosides are essential modified units of natural and synthetic nucleic acids[4]. 2-thiouracil could not inhibit the synthesis of TMV (tobacco mosaic virus) RNA, but could inhibit some early functions of TMV. 1 mM 2-thiouracil inhibited viral protein and RNA synthesis totally when treatment began within the first 4 h after initiation of replication, but not at all when treatment began at 12 h or later[5].
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