Edgar Alasdair J
Tissue Engineering and Regenerative Medicine Centre, Division of Investigative Science, Faculty of Medicine, Imperial College of Science, Technology and Medicine, Chelsea & Westminster Hospital, London, United Kingdom.
BMC Biochem. 2002 Jun 25;3:19. doi: 10.1186/1471-2091-3-19.
In mammals, L-threonine is an indispensable amino acid. The conversion of L-threonine to glycine occurs through a two-step biochemical pathway involving the enzymes L-threonine 3-dehydrogenase and 2-amino-3-ketobutyrate coenzyme A ligase. The L-threonine 3-dehydrogenase enzyme has been purified and characterised, but the L-threonine 3-dehydrogenase gene has not previously been identified in mammals.
Transcripts for L-threonine 3-dehydrogenase from both the mouse and pig are reported. The ORFs of both L-threonine dehydrogenase cDNAs encode proteins of 373 residues (41.5 kDa) and they share 80% identity. The mouse gene is located on chromosome 14, band C. The amino-terminal regions of these proteins have characteristics of a mitochondrial targeting sequence and are related to the UDP-galactose 4-epimerases, with both enzyme families having an amino-terminal NAD+ binding domain. That these cDNAs encode threonine dehydrogenases was shown, previously, by tiling 13 tryptic peptide sequences, obtained from purified L-threonine dehydrogenase isolated from porcine liver mitochondria, on to the pig ORF. These eukaryotic L-threonine dehydrogenases also have significant similarity with the prokaryote L-threonine dehydrogenase amino-terminus peptide sequence of the bacterium, Clostridium sticklandii. In murine tissues, the expression of both L-threonine dehydrogenase and 2-amino-3-ketobutyrate coenzyme A ligase mRNAs were highest in the liver and were also present in brain, heart, kidney, liver, lung, skeletal muscle, spleen and testis.
The first cloning of transcripts for L-threonine dehydrogenase from eukaryotic organisms are reported. However, they do not have any significant sequence homology to the well-characterised Escherichia coli L-threonine dehydrogenase.
在哺乳动物中，L-苏氨酸是一种必需氨基酸。L-苏氨酸向甘氨酸的转化通过一个两步生化途径进行，该途径涉及L-苏氨酸3-脱氢酶和2-氨基-3-酮丁酸辅酶A连接酶。L-苏氨酸3-脱氢酶已被纯化和表征，但此前在哺乳动物中尚未鉴定出L-苏氨酸3-脱氢酶基因。
报道了来自小鼠和猪的L-苏氨酸3-脱氢酶转录本。两种L-苏氨酸脱氢酶cDNA的开放阅读框均编码373个残基（41.5 kDa）的蛋白质，它们具有80%的同一性。小鼠基因位于14号染色体C带。这些蛋白质的氨基末端区域具有线粒体靶向序列的特征，并且与UDP-半乳糖4-表异构酶相关，这两个酶家族都有一个氨基末端NAD+结合结构域。此前，通过将从猪肝线粒体中分离的纯化L-苏氨酸脱氢酶获得的13个胰蛋白酶肽序列平铺到猪开放阅读框上，证明了这些cDNA编码苏氨酸脱氢酶。这些真核L-苏氨酸脱氢酶与艰难梭菌的原核L-苏氨酸脱氢酶氨基末端肽序列也有显著相似性。在小鼠组织中，L-苏氨酸脱氢酶和2-氨基-3-酮丁酸辅酶A连接酶mRNA的表达在肝脏中最高，在脑、心脏、肾脏、肝脏、肺、骨骼肌、脾脏和睾丸中也有表达。
报道了真核生物中L-苏氨酸脱氢酶转录本的首次克隆。然而，它们与已充分表征的大肠杆菌L-苏氨酸脱氢酶没有任何显著的序列同源性。
