Cd2+ activation of L-threonine dehydrogenase from Escherichia coli K-12.
Homogeneous preparations of L-threonine dehydrogenase (L-threonine:NAD+ oxidoreductase, EC 1.1.1.103) from Escherichia coli K-12, after having been dialyzed against buffers containing Chelex-100 resin, have a basal level of activity of 10-20 units/mg. Added Cd2+ stimulates dehydrogenase activity approx. 10-fold; this activation is concentration-dependent and is saturable with an activation Kd = 0.9 microM. Full activation by Cd2+ is obtained in the absence of added thiols. The pH-activity profile of the Cd2+-activated enzyme conforms to a theoretical curve for one-proton ionization with a pKa = 7.85. Mn2+, the only other activating metal ion, competes with Cd2+ for the same binding site. Km values for L-threonine and NAD+ as well as the Vmax for 'demetallized', Cd2+-activated, and Mn2+-activated threonine dehydrogenase were determined and compared.
Craig
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Department of Biological Chemistry, University of Michigan, Ann Arbor.
Dekker
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D000429:Alcohol Oxidoreductases / Q000378:metabolism*; D001667:Binding, Competitive; D002104:Cadmium / Q000037:antagonists & inhibitors / Q000378:metabolism / Q000494:pharmacology*; D004229:Dithiothreitol / Q000494:pharmacology; D004789:Enzyme Activation / Q000187:drug effects; D004926:Escherichia coli / Q000201:enzymology; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008345:Manganese / Q000378:metabolism; D008623:Mercaptoethanol / Q000494:pharmacology; D013438:Sulfhydryl Compounds
D013438:Sulfhydryl Compounds; D002104:Cadmium; D008345:Manganese; D008623:Mercaptoethanol; D000429:Alcohol Oxidoreductases; C023159:L-threonine 3-dehydrogenase; D004229:Dithiothreitol