PMID:3056527
| Citation |
Craig, PA and Dekker, EE (1988) Cd2+ activation of L-threonine dehydrogenase from Escherichia coli K-12. Biochim. Biophys. Acta 957:222-9 |
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| Abstract |
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. |
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| Keywords |
Alcohol Oxidoreductases/metabolism; Binding, Competitive; Cadmium/antagonists & inhibitors; Cadmium/metabolism; Cadmium/pharmacology; Dithiothreitol/pharmacology; Enzyme Activation/drug effects; Escherichia coli/enzymology; Hydrogen-Ion Concentration; Kinetics; Manganese/metabolism; Mercaptoethanol/pharmacology; Sulfhydryl Compounds |
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