• Journal of Microbiology and Biotechnology
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• v.24 no.6
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• pp.748-755
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• 2014

In the genome annotation of Escherichia coli MG1655, the orf382 (1,149 bp) is designated as a gene encoding an alcohol dehydrogenase that may be Fe-dependent. In this study, the gene was amplified from the genome by PCR and overexpressed in Escherichia coli BL21(DE3). The recombinant $6{\times}$His-tag protein was then purified and characterized. In an enzymatic assay using different hydroxyl-containing substrates (n-butanol, $\small{L}$-threonine, ethanol, isopropanol, glucose, glycerol, $\small{L}$-serine, lactic acid, citric acid, methanol, or $\small{D}$-threonine), the enzyme showed the highest activity on $\small{L}$-threonine. Characterization of the mutant constructed using gene knockout of the orf382 also implied the function of the enzyme in the metabolism of $\small{L}$-threonine into glycine. Considering the presence of tested substrates in living E. coli cel ls and previous literature, we believed that the suitable nomenclature for the enzyme should be an $\small{L}$-threonine dehydrogenase (LTDH). When using $\small{L}$-threonine as the substrate, the enzyme exhibited the best catalytic performance at $39^{\circ}C$ and pH 9.8 with $NAD^+$ as the cofactor. The determination of the Km values towards $\small{L}$-threonine (Km = $11.29{\mu}M$), ethanol ($222.5{\mu}M$), and n-butanol ($8.02{\mu}M$) also confirmed the enzyme as an LTDH. Furthermore, the LTDH was shown to be an ion-containing protein based on inductively coupled plasma-atomic emission spectrometry with an isoelectronic point of pH 5.4. Moreover, a circular dichroism analysis revealed that the metal ion was structurally and enzymatically essential, as its deprivation remarkably changed the ${\alpha}$-helix percentage (from 12.6% to 6.3%).

• Proceedings of the Korean Society of Applied Pharmacology
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• 2002.07a
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• pp.236-236
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• 2002

Pyruvate dehydrogenase phosphatase (PDP) is a mitochondrial protein serine/threonine phosphatase that catalyzes the dephosphorylation and concomitant reactivation of the pyruvate dehydrogenase componant of the pyruvate dehydrogenase complex (PDC). PDP consists of a Mg$\^$+2/ -dependent and Ca$\^$+2)-stimulated catalytic subunit (PDPc) of Mr 52,600 and a FAD-containing regulatory subunit (PDPr) of Mr 95.600. Catalytic subunit of pyruvate dehydrogenase phosphatase (PDPc) has been suggested to have three major functional domains such as dihydrolipoamide acetyltransferase(E$_2$)-binding domain, regulatory subunit of PDP(PDPr)-binding domain, and calcium-binding domain. In order to identify functional domains, recombinant catalytic subunit of pyruvate dehydrogenase phosphatase (rPDPc) was expressed in E. coli JM101 and purified to near homogeneity using the unique property of PDPc: PDPm binds to the inner lipoyl domain (L$_2$) of E$_2$ of pyruvate dehydrogenase complex (PDC) in the presence of Ca$\^$+2/, not under EGTA. PDPc was limited-proteolysed by trypsin, chymotrypsin, Arg-C, and elastase at pH7.0 and 30$^{\circ}C$ and N-terminal analysis of the fragment was done. Chymotrypsin, trypsin, and elastase made two major framents: N-terminal large fragment, approx. 50kD and C-terminal small fragment, approx. 0 kDa. Arg-C made three major fragments: N-terminal fragment, approx. 35 kD, and central fragment, approx. 15 kD, and C-terminal fragment, approx. 10 kD. This study strongly suggest that PDPc consists of three major functional domains. However, further study should be necessary to identify the functional role.