Effects of divalent cations and nucleotides on the 14CO2-oxaloacetate exchange catalyzed by the phosphoenol pyruvate carboxykinase from the moderate halophile, Vibrio costicola
| Autor: | M S, Salvarrey, J J, Cazzulo, J J, Cannata |
|---|---|
| Rok vydání: | 1995 |
| Předmět: |
Radioisotope Dilution Technique
Hot Temperature Oxaloacetates Cations Divalent Magnesium Chloride Drug Synergism Carbon Dioxide Ribonucleotides Substrate Specificity Enzyme Activation Kinetics Adenosine Triphosphate Cadmium Chloride Chlorides Manganese Compounds Phosphoenolpyruvate Carboxykinase (GTP) Carbon Radioisotopes Cadmium Vibrio |
| Zdroj: | Biochemistry and molecular biology international. 36(6) |
| ISSN: | 1039-9712 |
| Popis: | The phosphoenolpyruvate carboxykinase (PEPCK) from Vibrio costicola catalyzed a 14CO2-oxaloacetate exchange reaction with an unusual nucleotide specificity. ATP gave the higher apparent catalytic efficiency (Vmax/Km, 6.78), followed by GTP (1.30), CTP (0.87) and ITP (0.66). Maximal activity required a divalent cation; CdCl2 and MgCl2 synergistically activated the enzyme, when added in the presence of MnCl2. The sigmoidal saturation curve for MnCl2 (apparent n 2.11) was converted into a hyperbola by 0.01 mM CdCl2 (apparent n 1). The results suggest a double role of the divalent cation in the reaction mechanism, namely as part of the MeATP2- substrate and as free Me2+. Mn2+ would be the best for the first, and Cd2+ for the second role. Preincubation with 0.01 mM CdCl2 increased the activity of the enzyme assayed with MgATP2- through an increase in Vmax; addition of CdCl2 to the reaction mixture elicited further activation, through a 17-fold decrease in the apparent Km for MgATP2-. These results, together with the biphasic curve of activation by CdCl2 when used alone, suggest the existence of two different sites for free Cd2+ on the enzyme. |
| Databáze: | OpenAIRE |
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