PMID:2007567
| Citation |
Epperly, BR and Dekker, EE (1991) L-threonine dehydrogenase from Escherichia coli. Identification of an active site cysteine residue and metal ion studies. J. Biol. Chem. 266:6086-92 |
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| Abstract |
Pure L-threonine dehydrogenase from Escherichia coli is a tetrameric protein (Mr = 148,000) with 6 half-cystine residues/subunit; its catalytic activity as isolated is stimulated 5-10-fold by added Mn2+ or Cd2+. The peptide containing the 1 cysteine/subunit which reacts selectively with iodoacetate, causing complete loss of enzymatic activity, has been isolated and sequenced; this cysteine residue occupies position 38. Neutron activation and atomic absorption analyses of threonine dehydrogenase as isolated in homogeneous form now show that it contains 1 mol of Zn2+/mol of enzyme subunit. Removal of the Zn2+ with 1,10-phenanthroline demonstrates a good correlation between the remaining enzymatic activity and the zinc content. Complete removal of the Zn2+ yields an unstable protein, but the native metal ion can be exchanged by either 65Zn2+, Co2+, or Cd2+ with no change in specific catalytic activity. Mn2+ added to and incubated with the native enzyme, the 65Zn2(+)-, the Co2(+)-, or the Cd2(+)- substituted form of the enzyme stimulates dehydrogenase activity to the same extent. These studies along with previously observed structural homologies further establish threonine dehydrogenase of E. coli as a member of the zinc-containing long chain alcohol/polyol dehydrogenases; it is unique among these enzymes in that its activity is stimulated by Mn2+ or Cd2+. |
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| Keywords |
Alcohol Oxidoreductases/isolation & purification; Alcohol Oxidoreductases/metabolism; Amino Acid Sequence; Amino Acids/analysis; Binding Sites; Cations; Chelating Agents; Chromatography, High Pressure Liquid; Cysteine/metabolism; Enzyme Activation; Escherichia coli/enzymology; Metals/metabolism; Molecular Sequence Data; Peptide Mapping; Sequence Homology, Nucleic Acid; Spectrophotometry, Atomic |
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